Semiconductor device

ABSTRACT

Disclosed is a semiconductor device having a structure capable of reducing the self-inductance of internal wiring. The semiconductor device includes: a lower board having a lower conductor layer formed on the surface thereof; a switching element bonded to the lower conductor layer in an element bonding area; a terminal bonded to the lower conductor layer in a terminal bonding area; an upper board stacked on the lower board in a board bonding area between the element bonding area and the terminal bonding area, and having an upper conductor layer on the surface thereof; and a switching element connecting member which connects the switching element with the upper conductor layer.

This is a divisional application of U.S. application Ser. No.13/320,238, accorded with a 371(c) filing date of Apr. 27, 2012, andallowed on May 20, 2015, which was a National Stage application ofInternational Application PCT/JP2010/058049 having the InternationalFiling Date of May 12, 2010, the subject matters of which areincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a semiconductor device such as a powermodule.

BACKGROUND ART

A power module is a device for which a pair of switching elements areconnected in series to a power supply, and which obtains an output frombetween the pair of switching elements. Such a power module is used for,for example, an inverter circuit that forms a driving circuit to drivean electric motor. The electric motor is used as, for example, a powersource of an electric vehicle (including a hybrid car), a train, anindustrial robot, and the like. The power module is also applied to aninverter circuit that converts electric power generated by a solarbattery, a wind power generator, and other power generators(particularly, a private electric generator) so as to be consistent withthe electric power of a commercial power supply.

For the switching elements of power modules, devices using Si (silicon)semiconductors have been conventionally used. However, there has been aproblem of losses in the devices at the time of power conversion, andthe situation is that a further improvement in efficiency of the devicesusing Si materials is no longer feasible.

Therefore, a power module using as its switching elements power devicesusing SiC (silicon carbide) semiconductors has been proposed. The SiCpower devices are capable of a high-speed ON/OFF operation because theswitching speed is high. Consequently, a current quickly decreases atthe time of switch-off, so that switching loss can be reduced.

However, high-speed switching by the SiC power devices causes a newproblem that an increase in surge voltage at the time of switchingoccurs.

The surge voltage V is, as shown in the following formula (A), given bya product of a self-inductance L which internal wiring of the powermodule has and a differential (di/dt) of a current i by a time t (acurrent change ratio per hour).V=L·(di/dt)  (A)

The higher the switching speed, the greater the change ratio (di/dt) ofthe current i, so that the surge voltage V is increased. When the surgevoltage loads the devices with a voltage not less than a breakdownvoltage, the devices may be broken. Moreover, when the surge voltage isgreat, there are also concerns of an increase in EMI (electromagneticinterference) noise and a reduction in reliability.

Therefore, in order to reduce surge voltage while applying high-speedswitching elements such as SiC devices, it is necessary to reduce theself-inductance L which the internal wiring of the power module has.This challenge is common not only to power modules but also tosemiconductor devices having switching elements. Of course, also insemiconductor devices having switching elements using Si semiconductors,a reduction in surge voltage is a significant challenge.

CITATION LIST Patent Literature

Patent Document 1: Japanese Published Unexamined Patent Application No.2002-026251

SUMMARY OF INVENTION Technical Problem

An object of this invention is to provide a semiconductor device havinga structure capable of effectively reducing the self-inductance ofinternal wiring.

Another object of this invention is to provide a semiconductor devicecapable of realizing a power module with a small self-inductance ofinternal wiring.

Still another object of this invention is to provide a semiconductordevice which allows terminal lead-out in a direction parallel to theprincipal surface of a board.

Still another object of this invention is to provide a semiconductordevice improved in reliability against an external force to be appliedto terminals.

Still another object of this invention is to provide a semiconductordevice capable of reducing self-inductance and capable of improving thereliability against heat cycle.

Solution to Problem

A semiconductor device according to a first aspect of this inventionincludes a lower board having a lower conductor layer formed on asurface thereof, a switching element bonded to the lower conductor layerin an element bonding area, a terminal bonded to the lower conductorlayer in a terminal bonding area, an upper board stacked on the lowerboard in a board bonding area between the element bonding area and theterminal bonding area, and having an upper conductor layer on a surfacethereof, and a switching element connecting member which connects theswitching element with the upper conductor layer.

According to this configuration, a current path provided by the lowerconductor layer that interconnects the terminal and the switchingelement and a current path that leads to the upper conductor layer viathe switching element connecting member from the switching element areclose to each other. Moreover, currents in reverse directions flow inthe current paths. Accordingly, inductances of the current paths are atleast partially cancelled out, so that a semiconductor device with a lowself-inductance of internal wiring can be provided. Accordingly, evenwhen the switching speed of the switching element is high, a surgevoltage can be suppressed. Consequently, a semiconductor device that iscapable of high-speed switching, has a small loss accordingly, and has ahigh breakdown voltage margin can be realized. Moreover, because heatgeneration at the time of high-frequency operation can be suppressed dueto a small loss, a semiconductor device that is unlikely to causethermal runaway can be provided. Further, because a surge voltage can besuppressed, an increase in EMI (electromagnetic interference) noise anda reduction in reliability can be avoided.

The switching element connecting member may be a metal wire made ofaluminum or other metals, may be a narrow band-shaped ribbon, and may bea lead frame made of a plate-like body. In any case, it is preferablethat the switching element connecting member is arranged so as toconnect the switching element and the upper conductor layer at a minimumdistance. Accordingly, the inductance of the internal wiring can bereduced.

The switching element may have a form of a MOS field-effect transistor.Silicon (Si) may be the semiconductor to be applied to the switchingelement, but it is preferable to apply a Sic (silicon carbide)semiconductor capable of high-speed operation.

The lower board may be a board for which a metal foil (for example, acopper foil) serving as a conductor layer is formed on the surface of aninsulating board. Specifically, the lower board may be a DBC (DirectBonding Copper) board for which a copper foil is directly bonded onto aceramic. Similarly, the upper board may be a board for which a metalfoil (for example, a copper foil) serving as a conductor layer is formedon the surface of an insulating board. That is, the upper board may be aDBC board for which a copper foil is directly bonded onto a ceramic.

In one embodiment of this invention, the upper conductor layer is formedin a rectangular shape, a plurality of switching elements are facing oneside of the rectangular-shaped upper conductor layer, and the switchingelements include a pair of switching elements facing both end portionsof the one side.

According to this configuration, because a pair of switching elementsare arranged facing both end portions of one side of the upper conductorlayer, the width as a whole (entire arrangement width) of switchingelement connecting members to connect the switching elements and theupper conductor layer can be increased (substantially maximized).Accordingly, the inductance due to the switching element connectingmembers can be reduced, so that the self-inductance due to the internalwiring of the semiconductor device can be further reduced.

When the switching element connecting member is made of a metal wire ora metal ribbon, it is preferable that a plurality of metal wires ormetal ribbons are arranged parallel to each other. Accordingly, theentire arrangement width can be increased (maximized).

In one embodiment of this invention, the semiconductor device furtherincludes a diode element bonded to the lower conductor layer in theelement bonding area, and a diode element connecting member whichconnects the diode element with the upper conductor layer.

According to this configuration, a current path provided by the lowerconductor layer that interconnects the terminal and the diode elementand a current path that leads to the upper conductor layer via the diodeelement connecting member from the diode element are close to eachother. Moreover, currents in reverse directions flow in the currentpaths. Accordingly, inductances of the current paths are at leastpartially cancelled out, so that a semiconductor device with a lowself-inductance of internal wiring can be provided. Accordingly, a surgevoltage can be suppressed, so that a semiconductor device that has ahigh breakdown voltage margin can be realized.

The diode element connecting member may be a metal wire made of aluminumor other metals, may be a narrow band-shaped ribbon, and may be a leadframe made of a plate-like body. In any case, it is preferable that thediode element connecting member is arranged so as to connect the diodeelement and the upper conductor layer at a minimum distance.Accordingly, the inductance of the internal wiring can be reduced.

In one embodiment of this invention, the upper conductor layer is formedin a rectangular shape, a plurality of diode elements are facing oneside of the rectangular-shaped upper conductor layer, and the diodeelements include a pair of diode elements facing both end portions ofthe one side.

According to this configuration, because a pair of diode elements arearranged facing both end portions of one side of the upper conductorlayer, the width as a whole (entire arrangement width) of diode elementconnecting members to connect the diode elements and the upper conductorlayer can be increased (substantially maximized). Accordingly, theinductance due to the diode element connecting members can be reduced,so that the self-inductance due to the internal wiring of thesemiconductor device can be further reduced.

When the diode element connecting member is made of a metal wire or ametal ribbon, it is preferable that a plurality of metal wires or metalribbons are arranged parallel to each other. Accordingly, the entirearrangement width can be increased (maximized).

In one embodiment of this invention, the switching element is an elementusing a SiC semiconductor. Due to this configuration, the switchingspeed of the switching element is increased, so that a switching losscan be reduced. Moreover, because the inductance of the internal wiringis low, a surge voltage can be suppressed. Consequently, a semiconductordevice that is capable of high-speed switching, has a small lossaccordingly, and has a high breakdown voltage margin can be realized.

In one embodiment of this invention, the switching element includes aplurality of switching elements, the element bonding area includes afirst area along one side of the upper conductor layer, a second areaextending from the first area in a direction to separate from the upperboard, and a third area extending from the first area in a direction toseparate from the first area at a position different from the secondarea, and at least one switching element is bonded to each of the firstarea, second area, and third area, and the semiconductor device furtherincludes a first controlling conductor layer arranged facing the firstarea, a second controlling conductor layer arranged facing the firstcontrolling conductor layer from an opposite side to the first area, andextending between the first controlling conductor layer and the secondarea and third area, and controlling wiring members for respectiveconnections between the switching elements arranged in the first area,second area and third area and the first controlling conductor layer andsecond controlling conductor layer.

Due to this configuration, intersection of the controlling wiringmembers with each other in a plan view from a normal direction of thelower board is avoided, while the switching elements can be connected tothe first and second controlling conductor layers. That is, becausethere is no need for a grade-separated intersection of the controllingwiring members with each other, the length of the controlling wiringmembers can be reduced.

A semiconductor device according to a second aspect of this inventionincludes a first lower board having a first lower conductor layer formedon a surface thereof, a first switching element bonded to the firstlower conductor layer in a first element bonding area, a first powersupply terminal bonded to the first lower conductor layer in a firstterminal bonding area, a first upper board stacked on the first lowerboard in a first board bonding area between the first element bondingarea and the first terminal bonding area, and having a first upperconductor layer on a surface thereof, a first switching elementconnecting member which connects the first switching element with thefirst upper conductor layer, a second lower board having a second lowerconductor layer formed on a surface thereof, a second switching elementbonded to the second lower conductor layer in a second element bondingarea, an output terminal electrically connected to the first upperconductor layer, and bonded to the second lower conductor layer in asecond terminal bonding area, a second upper board stacked on the secondlower board in a second board bonding area between the second elementbonding area and the second terminal bonding area, and having a secondupper conductor layer on a surface thereof, a second switching elementconnecting member which connects the second switching element with thesecond upper conductor layer, a second power supply terminal bonded tothe second upper conductor layer, and a holding base which holds thefirst lower board and the second lower board so that the first andsecond terminal bonding areas are adjacent to each other.

Due to this configuration, a power module for which the first and secondswitching elements are connected in series between the first and secondpower supply terminals, and the output terminal is connected between thefirst and second switching elements can be provided. In addition, acurrent path provided by the first lower conductor layer thatinterconnects the first power supply terminal and the first switchingelement and a current path that leads to the first upper conductor layervia the first switching element connecting member from the firstswitching element are close to each other. Moreover, currents in reversedirections flow in the current paths. Similarly, a current path providedby the second lower conductor layer that interconnects the outputterminal and the second switching element and a current path that leadsto the second power supply terminal through the second switching elementconnecting member and the second upper conductor layer from the secondswitching element are close to each other. Moreover, currents in reversedirections flow in the current paths. Accordingly, inductances of thecurrent paths are at least partially cancelled out, so that asemiconductor device (power module) with a low self-inductance ofinternal wiring can be provided. For example, a power module having aself-inductance of approximately 20 nH due to internal wiring can beprovided. Accordingly, even when the switching speed of the first andsecond switching elements is high, a surge voltage can be suppressed.Consequently, a semiconductor device (power module) that is capable ofhigh-speed switching, has a small loss accordingly, and has a highbreakdown voltage margin can be realized. Further, because the first andsecond lower boards are arranged adjacent to each other on the holdingbase, the connection wiring length therebetween is short. Also whereby,inductance can be reduced.

It is preferable that the holding base is formed of copper or othermaterials with high heat conductivity. Accordingly, the holding base canfunction as a heat radiating base to radiate heat generated by theswitching element to the outside. In this case, it is preferable that aheat sink or other cooling means are mounted on the holding base (heatradiating base).

The configurations described in relation to the semiconductor deviceaccording to the first aspect can be applied also to the semiconductordevice according to the second aspect.

In one embodiment of this invention, the first power supply terminal andsecond power supply terminal have plate-shaped parts facing each otherwith a predetermined interval kept therebetween. Due to thisconfiguration, inductances of the first and second power supplyterminals can be cancelled out by currents that flow through the firstand second power supply terminals in reverse directions to each other.Accordingly, the self-inductance can be reduced more.

A semiconductor device according to a third aspect includes a boardassembly including a semiconductor element and a board, a terminalbonded to the board assembly, and extending parallel to a principalsurface of the board, and a resin case which surrounds the wiring board,and the resin case is made of an assembly including a first casecomponent having an insertion hole through which the terminal isinserted and a second case component which is combined with the firstcase component. The semiconductor element may include a switchingelement, or may include a diode element.

According to this configuration, the terminal extends in a directionparallel to the principal surface of the board to be led out of theresin case. Accordingly, the terminal length can be reduced, which canaccordingly contribute to a reduction in inductance. On the other hand,the first case component of the resin case is formed with an insertionhole. By inserting the terminal through the insertion hole, the firstcase component can be combined with the second case component toassemble the resin case. Therefore, the resin case can be assembledafter bonding the terminal to the board assembly.

Because the terminal is led out parallel to the principal surface of theboard, if the resin case is an integrally molded piece, the resin casecannot be attached after bonding of the terminal. This problem is solvedby insert molding of the terminal together with the resin case, but inthis case, because the resin case is exposed to a high temperature atthe time of terminal bonding (for example, solder bonding), extremelyhigh heat resistance is required.

The semiconductor device according to the third aspect provides asolution to these problems.

Attachment of the first case component to the second case component maybe performed by, for example, screwing, or may be performed by adhesion.

A semiconductor device according to a fourth aspect includes a boardassembly including a semiconductor element and a board, a terminalhaving a bonding portion bonded to the board, a first rising portionrising from the bonding portion in a direction to separate from aprincipal surface of the board, a transverse portion extending from anupper end of the first rising portion along the principal surface of theboard, and a second rising portion rising from the transverse portion ina direction to separate from the principal surface of the board, aterminal pedestal arranged between the second rising portion and theprincipal surface of the board, and a terminal retainer arranged so asto make contact with or approximate the transverse portion from anopposite side to the principal surface of the board.

According to this configuration, the transverse portion is restrictedfrom displacement to the board side by the terminal pedestal, and thesecond rising portion is restricted from displacement to an oppositeside to the board by the terminal retainer. Accordingly, even if, forexample, an external force along a normal direction of the board acts onthe second rising portion, the second rising portion is not greatlydisplaced. Therefore, damage to the terminal and separation of bondingbetween the terminal and board can be inhibited or prevented, so that asemiconductor device excellent in reliability can be provided.

In one embodiment of this invention, the semiconductor device furtherincludes a case which surrounds the board assembly, and the caseincludes a case plate in which an insertion hole through which thesecond rising portion is inserted is formed, and the case plate isprovided with the terminal retainer. Due to this configuration, the caseplate (for example, a top plate of the case) is provided with theterminal retainer, so that displacement or deformation of the terminalcan be suppressed by the simple structure.

In one embodiment of this invention, the terminal retainer is an innersurface of the case plate facing the transverse portion, and the caseplate is attached to the case so that the inner surface is arrangedsubstantially flush with the transverse portion. According to thisconfiguration, the inner surface of the case plate (for example, a topplate of the case) functions as a terminal retainer, so that theconfiguration can be further simplified. Moreover, because a small casecan be realized, the semiconductor device can be downsized.

The configurations of the semiconductor device according to the thirdaspect and the semiconductor device according to the fourth aspect canalso be combined with the configuration of the semiconductor deviceaccording to the first aspect or the semiconductor device according tothe second aspect.

In one embodiment of this invention, the switching element connectingmember is a switching element connecting frame made of a plate-likebody. The switching element connecting frame made of a plate-like bodyhas a sectional area larger than that of bonding wires. For this reason,the self-inductance can be reduced more than in a structure for whichbonding wires are adopted as switching element connecting members.

In one embodiment of this invention, the semiconductor device furtherincludes a switching element connecting resilient member withconductivity interposed between the switching element and the switchingelement connecting frame, and a pressing member which presses theswitching element connecting frame to the switching element side so thatthe switching element connecting resilient member is pressed to theswitching element side by the switching element connecting frame.

In this configuration, the switching element connecting resilient memberwith conductivity is interposed between the switching element and theswitching element connecting frame. In addition, the switching elementconnecting frame is pressed by the pressing member to the switchingelement side so that the switching element connecting resilient memberis pressed to the switching element side by the switching elementconnecting frame. That is, a connection between the switching elementand the switching element connecting frame is achieved not by solderingbut as a result of the switching element connecting resilient memberbeing pressed to the switching element side by the switching elementconnecting frame. Therefore, even if a thermal expansion/contractiondifference occurs between the switching element and the switchingelement connecting frame, the thermal expansion/contraction differencecan be absorbed by deformation of the resilient member or a relativeshift between the switching element connecting frame and the switchingelement connecting resilient member. Thus, separation of the switchingelement connecting frame from the switching element can be prevented.Moreover, propagation of a stress caused by a thermalexpansion/contraction difference to the switching element can beprevented, and the occurrence of cracks of the switching elementresulting from the propagation of stress can be prevented. Therefore,according to this configuration, the self-inductance can be reduced, andreliability against heat cycle can be improved.

In one embodiment of this invention, the diode element connecting memberis a diode element connecting frame made of a plate-like body. The diodeelement connecting frame made of a plate-like body has a sectional arealarger than that of bonding wires. For this reason, the self-inductancecan be reduced more than in a structure for which bonding wires areadopted as diode element connecting members.

In one embodiment of this invention, the semiconductor device furtherincludes a diode element connecting resilient member with conductivityinterposed between the diode element and the diode element connectingframe, and a pressing member which presses the diode element connectingframe to the diode element side so that the diode element connectingresilient member is pressed to the diode element side by the diodeelement connecting frame.

In this configuration, a connection between the diode element and thediode element connecting frame is achieved not by soldering but as aresult of the diode element connecting resilient member being pressed tothe diode element side by the diode element connecting frame. Therefore,even if a thermal expansion/contraction difference occurs between thediode element and the diode element connecting frame, the thermalexpansion/contraction difference can be absorbed by deformation of theresilient member or a relative shift between the diode elementconnecting frame and the diode element connecting resilient member.Thus, separation of the diode element connecting frame from the diodeelement can be prevented. Moreover, propagation of a stress caused by athermal expansion/contraction difference to the diode element can beprevented, and the occurrence of cracks of the diode element resultingfrom the propagation of stress can be prevented. Therefore, according tothis configuration, the self-inductance can be reduced, and reliabilityagainst heat cycle can be improved.

In one embodiment of this invention, the switching element connectingmember and the diode element connecting member are a single elementconnecting frame made of a plate-like body. In this configuration, theself-inductance can be reduced more than in a structure for whichbonding wires are adopted as switching element connecting members anddiode element connecting members. Moreover, the switching element anddiode element can be connected to the upper conductor layer by the sameelement connecting frame, so that the number of components can bereduced, and a semiconductor device is easily manufactured.

In one embodiment of this invention, the semiconductor device furtherincludes a switching element connecting resilient member withconductivity interposed between the switching element and the elementconnecting frame, a diode element connecting resilient member withconductivity interposed between the diode element and the elementconnecting frame, and a pressing member which presses the elementconnecting frame to the switching element side and the diode elementside so that the switching element connecting resilient member ispressed to the switching element side and the diode element connectingresilient member is pressed to the diode element side by the elementconnecting frame.

In this configuration, a connection between the switching element anddiode element and the element connecting frame is achieved not bysoldering but as a result of the switching element connecting resilientmember and the diode element connecting resilient member being pressedby the element connecting frame to the switching element side and thediode element side, respectively. Therefore, even if a thermalexpansion/contraction difference occurs between the switching elementand diode element and the element connecting frame, the thermalexpansion/contraction difference can be absorbed by deformation of theresilient member or a relative shift between the element connectingframe and the resilient member. Thus, separation of the elementconnecting frame from the switching element or diode element can beprevented. Moreover, propagation of a stress caused by a thermalexpansion/contraction difference to the switching element and diodeelement can be prevented, and the occurrence of cracks of the switchingelement and diode element resulting from the propagation of stress canbe prevented. Therefore, according to this configuration, theself-inductance can be reduced, and reliability against heat cycle canbe improved.

The above and other objects, features, and advantages of the presentinvention will become apparent through the following description ofembodiments with reference to the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view showing an external appearance of a powermodule according to a first embodiment of this invention.

FIG. 2 is an illustrative perspective view for explaining aconfiguration of a power module circuit housed inside a case.

FIG. 3 is an illustrative plan view for explaining an arrangement ofcomponents of first and second board assemblies.

FIG. 4 is an electrical circuit diagram for explaining an electricalconfiguration of a power module.

FIG. 5A is an illustrative sectional view for explaining a current pathin an upper arm circuit (first board assembly), and FIG. 5B is anillustrative sectional view for explaining a current path in a lower armcircuit (second board assembly).

FIG. 6A is an illustrative side view for explaining an example of aholding structure of gate terminals and source sense terminals.

FIG. 6B is an illustrative side view for explaining another example of aholding structure of gate terminals and source sense terminals.

FIG. 7A is a view for explaining an effect of reducing inductance by areduction in the length of wires.

FIG. 7B is a view for explaining an effect of reducing inductance by anincrease in the entire arrangement width of wires.

FIG. 8 is a perspective view showing an external appearance of a powermodule according to a second embodiment of this invention.

FIG. 9 is an illustrative perspective view for explaining aconfiguration of a power module circuit housed inside a case.

FIG. 10 is a plan view of the configuration of FIG. 9.

FIG. 11 is an exploded perspective view of a case.

FIG. 12 is a perspective view for explaining a variation of terminals.

FIG. 13 is a perspective view for explaining a variation of terminals.

FIG. 14 is a perspective view for explaining a variation of terminals.

FIG. 15 is a perspective view for explaining a variation of terminals.

FIG. 16 is a perspective view for explaining a variation of terminals.

FIG. 17 is a perspective view for explaining a variation of terminals.

FIG. 18 is a perspective view for explaining a variation of terminals.

FIG. 19 is a perspective view for explaining a variation of terminals.

FIG. 20 is a perspective view for explaining a variation of terminals.

FIG. 21 is a perspective view for explaining a variation of terminals.

FIG. 22 is a perspective view for explaining a variation of terminals.

FIG. 23 is a perspective view for explaining a variation of terminals.

FIG. 24 is a perspective view for explaining a variation of terminals.

FIG. 25 is a perspective view for explaining a variation of terminals.

FIG. 26 is a perspective view for explaining a variation of terminals.

FIG. 27 is a perspective view for explaining a variation of terminals.

FIG. 28 is a perspective view for explaining a variation of terminals.

FIG. 29 is a perspective view for explaining a variation of terminals.

FIG. 30 is a perspective view for explaining a variation of terminals.

FIG. 31A is a schematic plan view showing an internal structure of apower module according to a third embodiment of the present invention,and FIG. 31B is a schematic side view of the internal structure of thepower module shown in FIG. 31A.

FIG. 32A is a schematic plan view showing an internal structure of apower module according to a fourth embodiment of the present invention,and FIG. 32B is a schematic side view of the internal structure of thepower module shown in FIG. 32A.

FIG. 33 is a schematic side view showing another configuration of aresilient member.

FIG. 34 is an illustrative perspective view for explaining aconfiguration of a power module circuit in a power module according to afifth embodiment of this invention.

FIG. 35 is an illustrative plan view showing first and second boardassemblies.

FIG. 36A is an illustrative sectional view showing a first boardassembly, and FIG. 36B is an illustrative sectional view showing asecond board assembly.

FIG. 37 is an illustrative perspective view for explaining aconfiguration of a power module circuit in a power module according to asixth embodiment of this invention.

FIG. 38 is an illustrative perspective view for explaining aconfiguration of a power module circuit in a power module according to aseventh embodiment of this invention.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of this invention will be described in detailwith reference to the accompanying drawings.

First Embodiment

FIG. 1 is a perspective view showing an external appearance of a powermodule according to a first embodiment of this invention. The powermodule 1 includes a heat radiating base 2, a case 3, a first powersupply terminal P, a second power supply terminal N, and an outputterminal OUT. For convenience of description, in the following, the +Xdirection, −X direction, +Y direction, −Y direction, +Z direction, and−Z direction shown in FIG. 1 may be used. The +X direction and the −Xdirection are two directions along a short side of the heat radiatingbase 2 having a rectangular shape in a plan view, and these directionsare simply called an “X direction” when collectively mentioned. The +Ydirection and the −Y direction are two directions along a long side ofthe heat radiating base 2, and these directions are simply called a “Ydirection” when collectively mentioned. The +Z direction and the −Zdirection are two directions along a normal of the heat radiating base2, and these directions are simply called a “Z direction” whencollectively mentioned. When the heat radiating base 2 is placed on ahorizontal plane, the X direction and the Y direction serve as twohorizontal directions (first horizontal direction and second horizontaldirection) along two horizontal straight lines (X-axis and Y-axis)perpendicular to each other, and the Z direction serves as a verticaldirection (height direction) along a vertical straight line (Z-axis).

The heat radiating base 2 is a plate-like body with a uniform thicknesshaving a rectangular shape in a plan view, and is made of a materialwith a high heat conductivity. More specifically, the heat radiatingbase 2 may be a copper base made of copper. The copper base may have anickel plating layer formed on its surface. At a principal surface of a−Z direction side of the heat radiating base 2, a heat sink or othercooling means are mounted, as necessary.

The case 3 is formed in a substantially rectangular parallelepipedshape, and is formed of a resin material. Particularly, it is preferableto use a heat resistant resin such as PPS (polyphenylene sulfide). Thecase 3 shows a rectangular shape substantially in alignment with theheat radiating base 2 in a plan view, and includes a frame portion 4fixed to one surface (a +Z direction-side surface) of the heat radiatingbase 2 and a top plate 5 fixed to the frame portion 4. The top plate 5blocks one side (a +Z direction side) of the frame portion 4, and facesthe principal surface of the heat radiating base 2 that blocks the otherside (a −Z direction side) of the frame portion 4. Accordingly, the heatradiating base 2, the frame portion 4, and the top plate 5 define acircuit housing space inside of the case 3. The frame portion 4 includesa pair of side plates 6, 7 and a pair of end plates 8, 9 that join bothends of the paired side plates 6, 7, respectively. The end plates 8, 9,in the vicinity of their respective intermediate portions, have recessportions 10, 11 that are recessed inward. In the recess portion 10, 11,the +Z direction-side surface of the heat radiating base 2 is exposed.In the exposed region, a mounting hole 12 that penetrates through theheat radiating base 2 in its thickness direction is formed. The powermodule 1 is, by a bolt (not shown) inserted through the mounting hole12, fixed to a predetermined fixing position of a mounting target. Theforegoing cooling means such as a heat sink may be mounted by using themounting hole 12. Recess portions 13, 14 are formed in the vicinity ofintermediate portions of a pair of end sides of the top plate 5 so as tobe in alignment with the recess portions 10, 11 of the end plates 8, 9.

On a +Z direction-side surface (outer surface) of the top plate 5, aterminal block 15 is formed. The terminal block 15 is arranged betweenthe recess portions 13, 14, and includes three terminal blocks 15P, 15N,and 15OUT aligned along the longitudinal direction (Y direction) of thetop plate 5. The three terminal blocks 15 are each formed in arectangular shape in a plan view, and provided with a hexagonalcylinder-shaped recess portion (not shown) opened in substantially thecenter. A nut (not shown) is embedded and fixed into the hexagonalcylinder-shaped recess portion.

On a surface (+Z direction-side surface) of the terminal block 15Parranged at one end, the first power supply terminal P is arranged.Moreover, on a surface (+Z direction-side surface) of the terminal block15N arranged at the middle, the second power supply terminal N isarranged. Further, on a surface (+Z direction-side surface) of theterminal block 15OUT arranged at the other end, the output terminal OUTis arranged.

The first power supply terminal P, the second power supply terminal N,and the output terminal OUT are each prepared by cutting out a metalplate (for example, a copper plate applied with nickel plating) into apredetermined shape, and applying thereto a bending process, and iselectrically connected to a circuit inside the case 3. Front endportions of the first power supply terminal P, the second power supplyterminal N, and the output terminal OUT are led out to the terminalblocks 15P, 15N, and 15OUT, respectively. The front end portions of thefirst power supply terminal P, the second power supply terminal N, andthe output terminal OUT are molded in band shapes, and molded so as toextend along the surfaces of the terminal blocks 15P, 15N, and 15OUT,respectively. The first power supply terminal P, the second power supplyterminal N, and the output terminal OUT have insertion holes 55 f, 56 d,57 f in their respective front end portions. By using bolts that areinserted through the insertion holes 55 f, 56 d, 57 f, and fitted byscrewing into the nuts described above, the terminals P, N, OUT can beconnected to a bus bar provided on the mounting target side of the powermodule 1.

FIG. 2 is an illustrative perspective view for explaining aconfiguration of a power module circuit housed inside of the case 3. Onthe heat radiating base 2, a first board assembly 20 that forms an upperarm (high-side) circuit 81 and a second board assembly 40 that forms alower arm (low-side) circuit 82 are arranged side by side in the Ydirection. The first power supply terminal P is connected to the firstboard assembly 20, and the second power supply terminal N is connectedto the second board assembly 40. The output terminal OUT is electricallyconnected to both of the first and second board assemblies 20, 40.

The first board assembly 20 includes a first lower board 21, a pluralityof first switching elements Tr1, a plurality of first diode elementsDi1, and a first upper board 22.

The first lower board 21 is formed in a rectangular shape in a planview, and is, in a position that its four sides are parallel to the foursides of the heat radiating base 2, respectively, bonded to one surface(+Z direction-side surface) of the heat radiating base 2. On a surface(a +Z direction-side surface) of the first lower board 21 of an oppositeside to the heat radiating base 2, a first lower conductor layer 23 isformed. The first lower board 21 is formed of, for example, a board(DBC: Direct Bonding Copper) for which a copper foil is directly bondedonto a ceramic. The first lower conductor layer 23 can be formed by thecopper foil. The first upper board 22 is bonded to the first lowerconductor layer 23, whereby the first upper board 22 is stacked on thefirst lower board 21. Moreover, to the first lower conductor layer 23,the first switching elements Tr1 and the first diode elements Di1 arebonded. Further, to the first lower conductor layer 23, a base endportion of the first power supply terminal P is bonded.

The first upper board 22 has a first upper conductor layer 24 on asurface (+Z direction-side surface) of an opposite side to the firstlower board 21. The first upper board 22 is formed of, for example, aboard (DBC) for which a copper foil is directly bonded onto a ceramic.The first upper conductor layer 24 can be formed by the copper foil. Thefirst upper conductor layer 24 and the first switching elements Tr1 andthe first diode elements Di1 are connected by a plurality of wires (forexample, aluminum wires) 25, 26, respectively. That is, the firstswitching elements Tr1 and the first diode elements Di1 are connected inparallel between the first lower conductor layer 23 and the first upperconductor layer 24.

On the surface (+Z direction-side surface) of the first lower board 21,a pair of controlling conductor layers 27, 28 are formed insulated fromthe first lower conductor layer 23. To the controlling conductor layers27, 28, a source sense terminal SS1 and a gate terminal G1 are bonded,respectively. The controlling conductor layers 27, 28 and the firstswitching elements Tr1 are connected therebetween by wires 31, 32,respectively.

The second board assembly 40 includes a second lower board 41, aplurality of second switching elements Tr2, a plurality of second diodeelements Di2, and a second upper board 42.

The second lower board 41 is formed in a rectangular shape in a planview, and is, in a position that its four sides are parallel to the foursides of the heat radiating base 2, respectively, bonded to one surface(+Z direction-side surface) of the heat radiating base 2. Moreover, thesecond lower board 41 is arranged close to a −Y direction side of thefirst lower board 21. On a surface (+Z direction-side surface) of thesecond lower board 41 of an opposite side to the heat radiating base 2,a second lower conductor layer 43 is formed. The second lower board 41is formed of, for example, a board (DBC) for which a copper foil isdirectly bonded onto a ceramic. The second lower conductor layer 43 canbe formed by the copper foil. The second upper board 42 is bonded to thesecond lower conductor layer 43, whereby the second upper board 42 isstacked on the second lower board 41. Moreover, to the second lowerconductor layer 43, the second switching elements Tr2 and the seconddiode elements Di2 are bonded. Further, to the second lower conductorlayer 43, a base end portion of the output terminal OUT is bonded.

The second upper board 42 has a second upper conductor layer 44 on asurface (+Z direction-side surface) of an opposite side to the secondlower board 41. The second upper board 42 is formed of, for example, aboard (DBC) for which a copper foil is directly bonded onto a ceramic.The second upper conductor layer 44 can be formed by the copper foil.The second upper conductor layer 44 and the second switching elementsTr2 and the second diode elements Di2 are connected by a plurality ofwires (for example, aluminum wires) 45, 46, respectively. That is, thesecond switching elements Tr2 and the second diode elements Di2 areconnected in parallel between the second lower conductor layer 43 andthe second upper conductor layer 44.

On the surface (+Z direction-side surface) of the second lower board 41,further, a pair of controlling conductor layers 47, 48 are formedinsulated from the first lower conductor layer 43. To the controllingconductor layers 47, 48, a source sense terminal SS2 and a gate terminalG2 are bonded, respectively. The controlling conductor layers 47, 48 andthe second switching elements Tr2 are connected therebetween by wires51, 52.

The first board assembly 20 and the second board assembly 40 areconnected by a connecting member 38 that is prepared by applying acut-out and bending process to a metal plate. The connecting member 38is formed in a band shape, its one end is bonded to the first upperconductor layer 24, and its other end is bonded to the second lowerconductor layer 43.

FIG. 3 is an illustrative plan view for explaining an arrangement ofcomponents of the first and second board assemblies 20, 40.

First, a configuration of the first board assembly 20 will be explained.In the first lower conductor layer 23 formed on the first lower board21, a first terminal bonding area 61 is arranged at a −X direction-sidemarginal portion. The base end portion of the first power supplyterminal P is bonded to the first terminal bonding area 61. Moreover, inthe first lower conductor layer 23, a first element bonding area 62 isarranged at a +X direction-side marginal portion. To the first elementbonding area 62, the first switching elements Tr1 and the first diodeelements Di1 are bonded. Between the first terminal bonding area 61 andthe first element bonding area 62, a first board bonding area 63 isarranged. In the first board bonding area 63, the first upper board 22is bonded to the first lower conductor layer 23.

The first lower conductor layer 23 is formed so as to coversubstantially the entire area of the surface (+Z direction-side surface)of the first lower board 21, and is formed as a roughly rectangularregion. The first lower conductor layer 23 has a rectangular cut-away 23a at the marginal portion on the first element bonding area 62 side. Thecut-away 23 a is formed in a shape recessed inward (−X direction) fromthe vicinity of the middle of one side (a side at the +X direction side)of the first lower conductor layer 23. The controlling conductor layers27, 28 are arranged in the cut-away 23 a.

The first element bonding area 62 has a first area 62 a facing one side(a side at the +X direction side) of the first upper board 22 and a pairof second areas 62 b, 62 c extending parallel to each other from bothend portions (both end portions in the Y direction) of the first area 62a in a direction (+X direction) to separate from the first upper board22. In the vicinity of both end portions (both end portions in the Ydirection) of the first area 62 a, a pair of first diode elements Di1are arranged, respectively. In the vicinity of the middle sandwiched bythe paired first diode elements Di1, a pair of first switching elementsTr1 are arranged side by side in the Y direction. That is, in the firstarea 62 a, a pair of first diode elements Di1 and a pair of firstswitching elements Tr1 are arranged aligned in the Y direction, andthese are facing one side of the first upper board 22. In the pair ofsecond areas 62 b, 62 c, first switching elements Tr1 are arranged oneeach. The pair of first switching elements Tr1 are, with respect to thepair of first diode elements Di1, arranged at the opposite side (+Xdirection side) to the first upper board 22, and are, in terms of thedirection (X direction) perpendicular to one side (a side at the +Xdirection side) of the first upper board 22, positionally in alignmentwith the pair of first diode elements Di1. That is, the pair of firstdiode elements Di1 and the pair of first switching elements Tr1 that arepositionally in alignment with the first diode elements Di1,respectively, in terms of the X direction are facing both end portionsof one side of the first upper board 22 (in other words, one side of thefirst upper conductor layer 24. A side at the +X direction side).

The first upper conductor layer 24 is formed in a rectangular shape oversubstantially the entire area of the surface (+Z direction-side surface)of the first upper board 22. In the first upper conductor layer 24, anarea facing the first element bonding area 62 is a wire bonding area 24a to which the wires 25, 26 are bonded, and an area facing the firstterminal bonding area 61 is an assembly interconnection area 24 b for aconnection with the second board assembly 40. To the wire bonding area24 a, one-side ends of the wires 25, 26 are bonded.

To a bonding pad (not shown) formed on an upper surface (+Zdirection-side surface) of each first diode element Di1, one-side endsof a plurality of (for example, five) wires 26 are bonded. Theother-side ends of the wires 26 are bonded to the first upper conductorlayer 24 at a plurality of positions aligned in the Y direction alongone side (a side at the +X direction side) of the first upper conductorlayer 24. The wires 26 form loops along the direction (X direction)perpendicular to one side (a side at the +X direction side) of the firstupper conductor layer 24 so as not to contact each other and so as tohave the minimum lengths. Therefore, the wires 26, along the Xdirection, pass through a path above the first lower conductor layer 23(a path separating in the +Z direction from the first lower conductorlayer 23) to connect the first diode elements Di1 with the first upperconductor layer 24.

Similarly, to a bonding pad (not shown) formed on an upper surface (+Zdirection-side surface) of each first switching element Tr1, one-sideends of a plurality of (for example, six) wires 25 are bonded. Theother-side ends of the wires 25 are bonded to the first upper conductorlayer 24 at a plurality of positions aligned in the Y direction alongone side (a side at the +X direction side) of the first upper conductorlayer 24. The wires 25 form loops along the direction (X direction)perpendicular to one side (a side at the +X direction side) of the firstupper conductor layer 24 so as not to contact each other and so as tohave the minimum lengths. Therefore, the wires 25, along the Xdirection, pass through a path above the first lower conductor layer 23(a path separating in the +Z direction from the first lower conductorlayer 23) to connect the first switching elements Tr1 with the firstupper conductor layer 24.

However, the wires 25 bonded to the pair of first switching elements Tr1arranged in the second areas 62 b, 62 c of the first element bondingarea 62, respectively, pass through a path above the wires 26corresponding to the first diode elements Di1 arranged in alignment inthe X direction (a path separating in the +Z direction) so as not tocontact with those wires 26. Further, those wires 25 are bonded to thefirst upper conductor layer 24 at positions further on the firstterminal bonding area 61 side (−X direction side) than those of thewires 26. In FIG. 3, for the sake of clarification, the wires 25 of thefirst switching elements Tr1 arranged in the second areas 62 b, 62 c areshown with their halfway portions omitted.

As described above, the wires 26 to connect the first diode elements Di1to the first upper conductor layer 24 are arranged so as to have theminimum lengths, respectively. Further, the arrangement width of thewires 26 as a whole (the width in the Y direction. Hereinafter, referredto as an “entire arrangement width.”) covers substantially the entirewidth of one side (a side at the +X direction side) of the first upperconductor layer 24. Similarly, as described above, the wires 25 toconnect the first switching elements Tr1 to the first upper conductorlayer 24 are arranged so as to have the minimum lengths, respectively.Further, the arrangement width of the wires 25 as a whole (the width inthe Y direction. Entire arrangement width) covers substantially theentire width of one side (a side at the +X direction side) of the firstupper conductor layer 24.

The controlling conductor layer 27 corresponding to the source senseterminal SS1 has a rectangular shape facing the first area 62 a of thefirst element bonding area 62, and extending in the direction (Ydirection) parallel to one side (a side at the +X direction side) of thefirst upper conductor layer 24. In the vicinity of the center of thecontrolling conductor layer 27, the source sense terminal SS1 is bonded.

The controlling conductor layer 28 corresponding to the gate terminal G1is, in a plan view in the −Z direction, formed in a substantiallyU-shape holding the controlling conductor layer 27 inside. That is, thecontrolling conductor layer 28 has a central portion 28 a that faces thecontrolling conductor layer 27 from the opposite side (+X directionside) to the first area 62 a of the first element bonding area 62 and apair of arm portions 28 b, 28 c that extend from both end portions ofthe central portion 28 a in the −X direction toward the first area 62 a.The central portion 28 a extends in the Y direction, and in the vicinityof its center, the gate terminal G1 is bonded. The pair of arm portions28 b, 28 c pass between the controlling conductor layer 27 and thesecond area 62 b and the third area 62 c of the first element bondingarea 62, respectively, and reach the neighborhood of the first area 62a.

The first switching elements Tr1 are, via the wires 31, respectively,connected to the controlling conductor layer 27 for the source senseterminal SS1. The wires 31 corresponding to, out of the first switchingelements Tr1, the pair of first switching elements Tr1 arranged in thefirst area 62 a are bonded at one-side ends to the first switchingelements Tr1, and bonded at the other-side ends to the controllingconductor layer 27 in the neighborhood of one side (a side at the −Xdirection side) facing the first area 62 a. The wires 31 form loopsalong the X direction so as to have the minimum lengths. On the otherhand, the wires 31 corresponding to, out of the first switching elementsTr1, the pair of first switching elements Tr1 arranged in the secondareas 62 b, 62 c pass through a path above the arm portions 28 b, 28 cof the controlling conductor layer 28 (a path separating in the +Zdirection from the controlling conductor layer 28). The wires 31 arebonded at one-side ends to the first switching elements Tr1, and bondedat the other-side ends to the controlling conductor layer 27 in theneighborhood of sides (a side at the −Y direction side and a side at the+Y direction side) facing the second areas 62 b, 62 c, respectively. Thewires 31 form loops along the Y direction so as to have the minimumlengths.

Further, the first switching elements Tr1 are, via the wires 32,respectively, connected to the controlling conductor layer 28 for thegate terminal G1. The wires 32 corresponding to, out of the firstswitching elements Tr1, the pair of first switching elements Tr1arranged in the first area 62 a are bonded at one-side ends to the firstswitching elements Tr1, and bonded at the other-side ends to front endportions of the pair of arm portions 28 b, 28 c of the controllingconductor layer 28, respectively. The bonding positions are locatedfurther on the first upper board 22 side (−X direction side) than thepath of the wires 31 led out of the pair of first switching elements Tr1arranged in the second areas 62 b, 62 c. Therefore, the wires 31, 32 donot intersect each other in a plan view. The wires 32 form loops alongthe X direction so as to have the minimum lengths. On the other hand,the wires 32 corresponding to, out of the first switching elements Tr1,the pair of first switching elements Tr1 arranged in the second areas 62b, 62 c are connected to base end portions of the arm portions 28 b, 28c of the controlling conductor layer 28, respectively. The wires 32 arebonded at one-side ends to the first switching elements Tr1, and bondedat the other-side ends to the base end portions (+X direction-side endportions) of the arm portions 28 b, 28 c of the controlling conductorlayer 28. The wires 32 form loops along the Y direction so as to havethe minimum lengths.

Next, a configuration of the second board assembly 40 will be explained.In the second lower conductor layer 43 formed on the second lower board41, a second terminal bonding area 71 is arranged at a −X direction-sidemarginal portion. The base end portion of the output terminal OUT isbonded to the second terminal bonding area 71. Moreover, in the secondlower conductor layer 43, a second element bonding area 72 is arrangedat a +X direction-side marginal portion. To the second element bondingarea 72, the second switching elements Tr2 and the second diode elementsDi2 are bonded. Between the second terminal bonding area 71 and thesecond element bonding area 72, a second board bonding area 73 isarranged. In the second board bonding area 73, the second upper board 42is bonded to the second lower conductor layer 43.

The second lower conductor layer 43 is formed so as to coversubstantially the entire area of the surface (+Z direction-side surface)of the second lower board 41, and is formed as a roughly rectangularregion. The second lower conductor layer 43 has a rectangular cut-away43 a at the marginal portion on the second element bonding area 72 side.The cut-away 43 a is formed in a shape recessed inward (−X direction)from the vicinity of the middle of one side (a side at the +X directionside) of the second lower conductor layer 43. The controlling conductorlayers 47, 48 are arranged in the cut-away 43 a.

The second element bonding area 72 has a first area 72 a facing one side(a side at the +X direction side) of the second upper board 42 and apair of second areas 72 b, 72 c extending parallel to each other fromboth end portions (both end portions in the Y direction) of the firstarea 72 a in a direction (+X direction) to separate from the secondupper board 42. In the vicinity of both end portions (both end portionsin the Y direction) of the first area 72 a, a pair of second diodeelements Di2 are arranged, respectively. In the vicinity of the middlesandwiched by the paired second diode elements Di2, a pair of secondswitching elements Tr2 are arranged side by side in the Y direction.That is, in the first area 72 a, a pair of second diode elements Di2 anda pair of second switching elements Tr2 are arranged aligned in the Ydirection, and these are facing one side of the second upper board 42.In the pair of second areas 72 b, 72 c, second switching elements Tr2are arranged one each. The pair of second switching elements Tr2 are,with respect to the pair of second diode elements Di2, arranged at theopposite side (+X direction side) to the second upper board 42, and are,in terms of the direction (X direction) perpendicular to one side (aside at the +X direction side) of the second upper board 42,positionally in alignment with the pair of second diode elements Di2.That is, the pair of second diode elements Di2 and the pair of secondswitching elements Tr2 that are positionally in alignment with thesecond diode elements Di2, respectively, in terms of the X direction arefacing both end portions of one side of the second upper board 42 (inother words, one side of the second upper conductor layer 44. A side atthe +X direction side).

The second upper conductor layer 44 is formed in a rectangular shapeover substantially the entire area of the surface (+Z direction-sidesurface) of the second upper board 42. In the second upper conductorlayer 44, an area facing the second element bonding area 72 is a wirebonding area 44 a to which the wires 45, 46 are bonded, and an areafacing the second terminal bonding area 71 is a terminal bonding area 44b to which the second power supply terminal N is bonded. To the wirebonding area 44 a, one-side ends of the wires 45, 46 are bonded.

To a bonding pad (not shown) formed on an upper surface (+Zdirection-side surface) of each second diode element Di2, one-side endsof a plurality of (for example, five) wires 46 are bonded. Theother-side ends of the wires 46 are bonded to the second upper conductorlayer 44 at a plurality of positions aligned in the Y direction alongone side (a side at the +X direction side) of the second upper conductorlayer 44. The wires 46 form loops along the direction (X direction)perpendicular to one side (a side at the +X direction side) of thesecond upper conductor layer 44 so as not to contact each other and soas to have the minimum lengths. Therefore, the wires 46, along the Xdirection, pass through a path above the second lower conductor layer 43(a path separating in the +Z direction from the second lower conductorlayer 43) to connect the second diode elements Di2 with the second upperconductor layer 44.

Similarly, to a bonding pad (not shown) formed on an upper surface (+Zdirection-side surface) of each second switching element Tr2, one-sideends of a plurality of (for example, six) wires 45 are bonded. Theother-side ends of the wires 45 are bonded to the second upper conductorlayer 44 at a plurality of positions aligned in the Y direction alongone side (a side at the +X direction side) of the second upper conductorlayer 44. The wires 45 form loops along the direction (X direction)perpendicular to one side (a side at the +X direction side) of thesecond upper conductor layer 44 so as not to contact each other and soas to have the minimum lengths. Therefore, the wires 45, along the Xdirection, pass through a path above the second lower conductor layer 43(a path separating in the +Z direction from the second lower conductorlayer 43) to connect the second switching elements Tr2 with the secondupper conductor layer 44.

However, the wires 45 bonded to the pair of second switching elementsTr2 arranged in the second areas 72 b, 72 c of the second elementbonding area 72, respectively, pass through a path above the wires 46corresponding to the second diode elements Di2 arranged in alignment inthe X direction (a path separating in the +Z direction) so as not tocontact with those wires 46. Further, those wires 45 are bonded to thesecond upper conductor layer 44 at positions further on the secondterminal bonding area 71 side (−X direction side) than those of thewires 46. In FIG. 3, for the sake of clarification, the wires 45 of thesecond switching elements Tr2 arranged in the second areas 72 b, 72 care shown with their halfway portions omitted.

As described above, the wires 46 to connect the second diode elementsDi2 to the second upper conductor layer 44 are arranged so as to havethe minimum lengths, respectively. Further, the arrangement width of thewires 46 as a whole (the width in the Y direction. Hereinafter, referredto as an “entire arrangement width.”) covers substantially the entirewidth of one side (a side at the +X direction side) of the second upperconductor layer 44. Similarly, as described above, the wires 45 toconnect the second switching elements Tr2 to the second upper conductorlayer 44 are arranged so as to have the minimum lengths, respectively.Further, the arrangement width of the wires 45 as a whole (the width inthe Y direction. Entire arrangement width) covers substantially theentire width of one side (a side at the +X direction side) of the secondupper conductor layer 44.

The controlling conductor layer 47 corresponding to the source senseterminal SS2 has a rectangular shape facing the first area 72 a of thesecond element bonding area 72, and extending in the direction (Ydirection) parallel to one side (a side at the +X direction side) of thesecond upper conductor layer 44. In the vicinity of the center of thecontrolling conductor layer 47, the source sense terminal SS2 is bonded.

The controlling conductor layer 48 corresponding to the gate terminal G2is, in a plan view in the −Z direction, formed in a substantiallyU-shape holding the controlling conductor layer 47 inside. That is, thecontrolling conductor layer 48 has a central portion 48 a that faces thecontrolling conductor layer 47 from the opposite side (+X directionside) to the first area 72 a of the second element bonding area 72 and apair of arm portions 48 b, 48 c that extend from both end portions ofthe central portion 48 a in the −X direction toward the first area 72 a.The central portion 48 a extends in the Y direction, and in the vicinityof its center, the gate terminal G2 is bonded. The pair of arm portions48 b, 48 c pass between the controlling conductor layer 47 and thesecond area 72 b and the third area 72 c of the second element bondingarea 72, respectively, and reach the neighborhood of the first area 72a.

The second switching elements Tr2 are, via the wires 51, respectively,connected to the controlling conductor layer 47 for the source senseterminal SS2. The wires 51 corresponding to, out of the second switchingelements Tr2, the pair of second switching elements Tr2 arranged in thefirst area 72 a are bonded at one-side ends to the second switchingelements Tr2, and bonded at the other-side ends to the controllingconductor layer 47 in the neighborhood of one side (a side at the −Xdirection side) facing the first area 72 a. The wires 51 form loopsalong the X direction so as to have the minimum lengths. On the otherhand, the wires 51 corresponding to, out of the second switchingelements Tr2, the pair of second switching elements Tr2 arranged in thesecond areas 72 b, 72 c pass through a path above the arm portions 48 b,48 c of the controlling conductor layer 48 (a path separating in the +Zdirection from the controlling conductor layer 48). The wires 51 arebonded at one-side ends to the second switching elements Tr2, and bondedat the other-side ends to the controlling conductor layer 47 in theneighborhood of sides (a side at the −Y direction side and a side at the+Y direction side) facing the second areas 72 b, 72 c, respectively. Thewires 51 form loops along the Y direction so as to have the minimumlengths.

Further, the second switching elements Tr2 are, via the wires 52,respectively, connected to the controlling conductor layer 48 for thegate terminal G2. The wires 52 corresponding to, out of the secondswitching elements Tr2, the pair of second switching elements Tr2arranged in the first area 72 a are bonded at one-side ends to thesecond switching elements Tr2, and bonded at the other-side ends tofront end portions of the pair of arm portions 48 b, 48 c of thecontrolling conductor layer 48, respectively. The bonding positions arelocated further on the second upper board 42 side (−X direction side)than the path of the wires 51 led out of the pair of second switchingelements Tr2 arranged in the second areas 72 b, 72 c. Therefore, thewires 51, 52 do not intersect each other in a plan view. The wires 52form loops along the X direction so as to have the minimum lengths. Onthe other hand, the wires 52 corresponding to, out of the secondswitching elements Tr2, the pair of second switching elements Tr2arranged in the second areas 72 b, 72 c are connected to base endportions of the arm portions 48 b, 48 c of the controlling conductorlayer 48, respectively. The wires 52 are bonded at one-side ends to thesecond switching elements Tr2, and bonded at the other-side ends to thebase end portions (+X direction-side end portions) of the arm portions48 b, 48 c of the controlling conductor layer 48. The wires 52 formloops along the Y direction so as to have the minimum lengths.

Next, referring to FIG. 2 and FIG. 3, description will be given of thestructure of the first power supply terminal P, the second power supplyterminal N, the output terminal OUT, and the connecting member 38 willbe described.

The first power supply terminal P is formed of a conductive plate-likebody (for example, a copper plate applied with nickel plating). Thefirst power supply terminal P has a bonding portion 55 a bonded to thefirst lower conductor layer 23, a first rising portion 55 b joined tothe bonding portion 55 a, a transverse portion 55 c joined to the firstrising portion 55 b, a second rising portion 55 d joined to thetransverse portion 55 c, and a connection end 55 e joined to the secondrising portion 55 d.

The bonding portion 55 a is bonded to a region closer to the +Ydirection of the first terminal bonding area 61, and is formed in arectangular shape extending in the Y direction in a plan view. Thebonding portion 55 a is formed of a plate-like body parallel to thefirst lower conductor layer 23, and is joined to the first lowerconductor layer 23. The first rising portion 55 b rises in the +Zdirection from a −X direction-side edge portion of the bonding portion55 a. The first rising portion 55 b is formed of a band-shapedplate-like body along a plane (a Y-Z plane) parallel to the Y directionand the Z direction, and is formed with substantially the same width asthat of the bonding portion 55 a. The transverse portion 55 c is joinedto a +Z direction-side edge portion of the first rising portion 55 b,and extends in the +X direction. The transverse portion 55 c is formedof a band-shaped plate-like body parallel to the principal surface ofthe heat radiating base 2, and is formed with substantially the samewidth as that of the first rising portion 55 b. The second risingportion 55 d rises in the +Z direction from a +X direction-side edgeportion of the transverse portion 55 c, and penetrates through the topplate 5 (refer to FIG. 1) of the case 3. The second rising portion 55 dis formed of a band-shaped plate-like body along a plane (a Y-Z plane)parallel to the Y direction and the Z direction, and has substantiallythe same width as that of the transverse portion 55 c. The connectionend 55 e extends in the +X direction from a +Z direction-side end edgeof the second rising portion 55 d, and is along an upper surface of theterminal block 15P (refer to FIG. 1). The connection end 55 e is formedof a band-shaped plate-like body along the principal surface of the heatradiating base 2, has substantially the same width as that of the secondrising portion 55 d, and has an insertion hole 55 f for connection inits substantially central portion. When assembled, the connection end 55e is in a standing position (a position along a Y-Z plane) extended fromthe second rising portion 55 d. After the connection end 55 e in astanding position is inserted through a slit-shaped insertion hole 5P(refer to FIG. 1) formed in the top plate 5, the connection end 55 e isbent down, so that the connection end 55 e is brought into a proneposition along an X-Y plane.

The second power supply terminal N is formed of a conductive plate-likebody (for example, a copper plate applied with nickel plating). Thesecond power supply terminal N has a bonding portion 56 a, a risingportion 56 b, and a connection end 56 c. The bonding portion 56 a is, inthe terminal bonding area 44 b of the second upper conductor layer 44,bonded to a region closer to the +Y direction. The bonding portion 56 ais formed in a rectangular shape extending in the Y direction, and isformed of a band-shaped plate-like body. The rising portion 56 b isjoined to a +X direction-side edge portion of the bonding portion 56 a.The rising portion 56 b is formed of a plate-like body parallel to aplane (a Y-Z plane) including the Y direction and the Z direction, andis formed in a substantially crank shape when viewed from a normaldirection (X direction) of the plate-like body. That is, the risingportion 56 b rises in the +Z direction, further extends transversally inthe +Y direction, and then again rises in the +Z direction. Theconnection end 56 c is joined to a +Z direction-side edge portion of therising portion 56 b. The connection end 56 c extends in the +Xdirection, and is along an upper surface of the terminal block 15N(refer to FIG. 1). The connection end 56 c is formed of a band-shapedplate-like body along the principal surface of the heat radiating base2, and has an insertion hole 56 d for connection in its substantiallycentral portion. When assembled, the connection end 56 c is in astanding position (a position along a Y-Z plane) extended from therising portion 56 b. After the connection end 56 c in a standingposition is inserted through a slit-shaped insertion hole 5N (refer toFIG. 1) formed in the top plate 5, the connection end 56 c is bent down,so that the connection end 56 c is brought into a prone position alongan X-Y plane.

The output terminal OUT is formed of a conductive plate-like body (forexample, a copper plate applied with nickel plating). The outputterminal OUT has a bonding portion 57 a bonded to the second lowerconductor layer 43, a first rising portion 57 b joined to the bondingportion 57 a, a transverse portion 57 c joined to the first risingportion 57 b, a second rising portion 57 d joined to the transverseportion 57 c, and a connection end 57 e joined to the second risingportion 57 d.

The bonding portion 57 a is bonded to a region closer to the −Ydirection of the second terminal bonding area 71, and is formed in arectangular shape extending in the Y direction in a plan view. Thebonding portion 57 a is formed of a plate-like body parallel to thesecond lower conductor layer 43, and is bonded to the second lowerconductor layer 43. The first rising portion 57 b rises in the +Zdirection from a −X direction-side edge portion of the bonding portion57 a. The first rising portion 57 b is formed of a band-shapedplate-like body along a plane (a Y-Z plane) parallel to the Y directionand the Z direction, and is formed with substantially the same width asthat of the bonding portion 57 a. The transverse portion 57 c is joinedto a +Z direction-side edge portion of the first rising portion 57 b,and extends in the +X direction. The transverse portion 57 c is formedof a band-shaped plate-like body parallel to the principal surface ofthe heat radiating base 2, and is formed with substantially the samewidth as that of the first rising portion 57 b. The second risingportion 57 d rises in the +Z direction from a +X direction-side edgeportion of the transverse portion 57 c, and penetrates through the topplate 5 (refer to FIG. 1) of the case 3. The second rising portion 57 dis formed of a band-shaped plate-like body along a plane (a Y-Z plane)parallel to the Y direction and the Z direction, and has substantiallythe same width as that of the transverse portion 57 c. The connectionend 57 e extends in the +X direction from a +Z direction-side end edgeof the second rising portion 57 d, and is along an upper surface of theterminal block 15OUT (refer to FIG. 1). The connection end 57 e isformed of a band-shaped plate-like body along the principal surface ofthe heat radiating base 2, has substantially the same width as that ofthe second rising portion 57 d, and has an insertion hole 57 f forconnection in its substantially central portion. When assembled, theconnection end 57 e is in a standing position (a position along a Y-Zplane) extended from the second rising portion 57 d. After theconnection end 57 e in a standing position is inserted through aslit-shaped insertion hole 5OUT (refer to FIG. 1) formed in the topplate 5, the connection end 57 e is bent down, so that the connectionend 57 e is brought into a prone position along an X-Y plane.

The connecting member 38 is formed of a conductive plate-like body (forexample, a copper plate applied with nickel plating). The connectingmember 38 has a first bonding portion 58 a, a first rising portion 58 b,a transverse connecting portion 58 c, a second rising portion 58 d, anda second bonding portion 58 e. The first bonding portion 58 a is formedof a rectangular plate-like body parallel to a principal surface of thefirst upper board 22, and is bonded to a position closer to the −Ydirection (closer to the second board assembly 40) in the assemblyinterconnection area 24 b of the first upper conductor layer 24. Thefirst rising portion 58 b is joined to a −X direction-side edge portionof the first bonding portion 58 a, and rises up to a predeterminedheight in the +Z direction. The first rising portion 58 b is formed of aband-shaped plate-like body parallel to a plane (a Y-Z plane) along theY direction and the Z direction, and is formed with substantially thesame width as that of the first bonding portion 58 a. On the other hand,the second bonding portion 58 e is formed of a rectangular plate-likebody parallel to a principal surface of the second lower board 41, andis bonded to a position closer to the +Y direction (closer to the firstboard assembly 20) in the second terminal bonding area 71 of the secondlower conductor layer 43. The second rising portion 58 d is joined to a+Y direction-side edge portion of the second bonding portion 58 e, andrises up to the predetermined height in the +Z direction. The secondrising portion 58 d is formed of a band-shaped plate-like body parallelto a plane (an X-Z plane) along the X direction and the Z direction, andis formed with substantially the same width as that of the secondbonding portion 58 e. The transverse connecting portion 58 c is formedin a shape bent in a hook shape in a plan view in the −Z direction, itsone end is joined to the first rising portion 58 b, and its other end isjoined to the second rising portion 58 d. The transverse connectingportion 58 c is formed of a plate-like body parallel to the principalsurface of the heat radiating base 2. Because the first and secondbonding portions 58 a, 58 e are arranged in proximity, the connectingmember 38 interconnects the first and second board assemblies 20, 40with the minimum path length, thereby contributing to a reduction ininductance.

FIG. 4 is an electrical circuit diagram for explaining an electricalconfiguration of the power module 1. The first switching elements Tr1and the first diode elements Di1 included in the first board assembly 20are connected in parallel between the first lower conductor layer 23 andthe first upper conductor layer 24 to form an upper arm circuit(high-side circuit) 81. Similarly, the second switching elements Tr2 andthe second diode elements Di2 included in the second board assembly 40are connected in parallel between the second lower conductor layer 43and the second upper conductor layer 44 to form a lower arm circuit(low-side circuit) 82. The upper arm circuit 81 and the lower armcircuit 82 are connected in series between the high voltage-side firstpower supply terminal P and the low voltage-side second power supplyterminal N, and the output terminal OUT is connected to a connectionpoint 83 between the upper arm circuit 81 and the lower arm circuit 82.A half-bridge circuit is thus formed. The half-bridge circuit can beused as a single-phase bridge circuit. Alternatively, by connecting aplurality of (for example, three) half-bridge circuits (power modules 1)in parallel to a power supply, a multi-phase (for example, 3-phase)bridge circuit can be formed.

The first and second switching elements Tr1, Tr2 are, in thisembodiment, made of N-channel DMOS (Double-Diffused Metal OxideSemiconductor) field-effect transistors. Particularly, in thisembodiment, the first and second switching elements Tr1, Tr2 arehigh-speed switching MOSFETs (SiC-DMOS) made of SiC semiconductordevices.

Moreover, the first and second diode elements Di1, Di2 are, in thisembodiment, made of Schottky bather diodes. Particularly, in thisembodiment, the first and second diode elements Di1, Di2 are made of SiCsemiconductor devices (SiC-SBDs).

The drains of the first switching elements Tr1 and the cathodes of thefirst diode elements Di1 are connected in common to the first lowerconductor layer 23. Moreover, the sources of the first switchingelements Tr1 and the anodes of the first diode elements Di1 areconnected in common to the first upper conductor layer 24. Further, thegates of the first switching elements Tr1 are connected in common to thegate terminal G1. To the sources of the first switching elements Tr1,the source sense terminal SS1 is connected in common A current flowingfrom the output terminal OUT toward the first power supply terminal Pbypasses the first switching elements Tr1 to flow through the firstdiode elements Di1, whereby breakdown of the first switching elementsTr1 due to a reverse current is prevented.

On the other hand, the drains of the second switching elements Tr2 andthe cathodes of the second diode elements Di2 are connected in common tothe second lower conductor layer 43. Moreover, the sources of the secondswitching elements Tr2 and the anodes of the second diode elements Di2are connected in common to the second upper conductor layer 44. Further,the gates of the second switching elements Tr2 are connected in commonto the gate terminal G2. To the sources of the second switching elementsTr2, the source sense terminal SS2 is connected in common A currentflowing from the second power supply terminal N toward the outputterminal OUT bypasses the second switching elements Tr2 to flow throughthe second diode elements Di2, whereby breakdown of the second switchingelements Tr2 due to a reverse current is prevented.

FIG. 5A is an illustrative sectional view for explaining a current pathin the upper arm circuit 81 (first board assembly 20), andillustratively shows a cross section taken along a plane (an X-Z plane)including the X direction and the Z direction. The heat radiating base 2and the first lower board 21 are bonded to each other by amedium-temperature solder 85. The first lower board 21 includes as abase substrate an insulating substrate made of an insulating materialsuch as a ceramic. The first lower conductor layer 23 described above isformed on an upper surface (a +Z direction-side surface) of theinsulating substrate, and on a lower surface (a −Z direction-sidesurface) thereof, a bonding conductor layer 33 is formed. The bondingconductor layer 33 is made of, for example, a copper foil formed on thesurface of the first lower board 21. The bonding conductor layer 33 isbonded to the heat radiating base 2 via the medium-temperature solder85. The medium-temperature solder 85 is a solder whose melting pointbelongs to a medium temperature range of approximately 220° C.

To the first terminal bonding area 61 set at one-side end portion (a −Xdirection-side end portion) of the first lower conductor layer 23, thebase end portion of the first power supply terminal P is bonded by alow-temperature solder 86A. The low-temperature solder 86A is a solderwhose melting point is lower than the melting point of themedium-temperature solder 85, and belongs to a low temperature range ofapproximately 180° C.

To the first element bonding area 62 set at the other-side end portion(a +X direction-side end portion) of the first lower conductor layer 23,a first switching element Tr1 and a first diode element Di1(semiconductor chips) are bonded by a high-temperature solder 87A. Thefirst switching element Tr1 has a drain terminal at its lower surface(−Z direction-side surface) facing the first lower conductor layer 23,and has a source terminal and a gate terminal at its upper surface (+Zdirection-side surface) of an opposite side to the first lower conductorlayer 23. Therefore, the drain terminal is bonded to the first lowerconductor layer 23 by the high-temperature solder 87A. To the sourceterminal, a wire 25 is bonded. Although not shown in FIG. 5A, the gateterminal is bonded to a wire 32 (refer to FIG. 3), and the sourceterminal is bonded also to a wire 31. The first diode element Di1 has acathode terminal at its lower surface (−Z direction-side surface) facingthe first lower conductor layer 23, and has an anode terminal at itsupper surface (+Z direction-side surface) of an opposite side to thefirst lower conductor layer 23. Therefore, the cathode terminal isbonded to the first lower conductor layer 23 by the high-temperaturesolder 87A. To the anode terminal, a wire 26 is bonded. Thehigh-temperature solder 87A is a solder whose melting point is higherthan that of the medium-temperature solder 85, and belongs to a hightemperature range of approximately 300° C.

To the first board bonding area 63 set, on a surface (+Z direction-sidesurface) of the first lower conductor layer 23, between the firstterminal bonding area 61 and the first element bonding area 62, thefirst upper board 22 is bonded by a high-temperature solder 87B. Thefirst upper board 22 includes as a base substrate an insulatingsubstrate made of an insulating material such as a ceramic. The firstupper conductor layer 24 described above is formed on an upper surface(a +Z direction-side surface) of the insulating substrate, and on alower surface (a −Z direction-side surface) thereof, a bonding conductorlayer 34 is formed. The bonding conductor layer 34 is made of, forexample, a copper foil formed on the surface of the first upper board22. The bonding conductor layer 34 is bonded to the first lowerconductor layer 23 via the high-temperature solder 87B. Thehigh-temperature solder 87B is the same solder as the high-temperaturesolder 87A.

At a −X direction-side marginal portion of the first upper conductorlayer 24, the connecting member 38 is bonded by a low-temperature solder86B. The low-temperature solder 86B is the same solder as thelow-temperature solder 86A.

When the first switching element Tr1 conducts, a current that has flowedin from the first power supply terminal P flows in the +X directionthrough the first lower conductor layer 23, and reaches the firstswitching element Tr1. The current that has flowed through the firstswitching element Tr1 is turned back, flows in the −X direction throughthe wire 25, and reaches the first upper conductor layer 24. Inside thefirst upper conductor layer 24, a current flows in the −X directiontoward the connecting member 38. The current is led from the connectingmember 38 to the second lower conductor layer 43 of the second boardassembly 40, and is supplied from the output terminal OUT to a motor orother loads. A current flow at this time is shown in FIG. 5A.

On the other hand, when a reverse-direction voltage is applied with thefirst switching element Tr1 cut off, a current in the +X direction thatleads to the first diode element Di1 flows through the wire 26. Thecurrent that has flowed through the first diode element Di1 is turnedback, and flows in the −X direction through the first lower conductorlayer 23.

Thus, a current to flow in the first switching element Tr1 flows in the+X direction and a current from the first switching element Tr1 flows inthe −X direction, so that the current directions are reverse to eachother. In addition, the first lower conductor layer 23 that provides apath of the current to flow in the +X direction and the wire 25 and thefirst upper conductor layer 24 that provide a path of the current toflow in the −X direction are close to each other. Similarly, a currentto flow in the first diode element Di1 flows in the +X direction and acurrent from the first diode element Di1 flows in the −X direction, sothat the current directions are reverse to each other. In addition, thewire 26 and the first upper conductor layer 24 that provide a path ofthe current to flow in the +X direction and the first lower conductorlayer 23 that provides a path of the current to flow in the −X directionare close to each other. That is, the paths of currents that flow inreverse directions to each other are arranged closely. Accordingly, aself-inductance of the first lower conductor layer 23 andself-inductances of the wires 25, 26 and the first upper conductor layer24 are at least partially cancelled out by mutual inductancestherebetween. Accordingly, the inductance of the power module 1 can bereduced.

FIG. 5B is an illustrative sectional view for explaining a current pathin the lower arm circuit 82 (second board assembly 40), andillustratively shows a cross section taken along a plane (an X-Z plane)including the X direction and the Z direction. The heat radiating base 2and the second lower board 41 are bonded to each other by amedium-temperature solder 95. The second lower board 41 uses as a basesubstrate an insulating substrate made of an insulating material such asa ceramic. The second lower conductor layer 43 described above is formedon an upper surface (a +Z direction-side surface) of the insulatingsubstrate, and on a lower surface (a −Z direction-side surface) thereof,a bonding conductor layer 53 is formed. The bonding conductor layer 53is made of, for example, a copper foil formed on the surface of thesecond lower board 41. The bonding conductor layer 53 is bonded to theheat radiating base 2 via the medium-temperature solder 95. Themedium-temperature solder 95 is a solder whose melting point belongs toa medium temperature range of approximately 220° C.

To the second terminal bonding area 71 set at one-side end portion (a −Xdirection-side end portion) of the second lower conductor layer 43, thebase end portion of the output terminal OUT is bonded by alow-temperature solder 96A. The low-temperature solder 96A is a solderwhose melting point is lower than the melting point of themedium-temperature solder 95, and belongs to a low temperature range ofapproximately 180° C.

To the second element bonding area 72 set at the other-side end portion(+X direction-side end portion) of the second lower conductor layer 43,a second switching element Tr2 and a second diode element Di2(semiconductor chips) are bonded by a high-temperature solder 97A. Thesecond switching element Tr2 has a drain terminal at its lower surface(−Z direction-side surface) facing the second lower conductor layer 43,and has a source terminal and a gate terminal at its upper surface (+Zdirection-side surface) of an opposite side to the second lowerconductor layer 43. Therefore, the drain terminal is bonded to thesecond lower conductor layer 43 by the high-temperature solder 97A. Tothe source terminal, a wire 45 is bonded. Although not shown in FIG. 5B,the gate terminal is bonded to a wire 52 (refer to FIG. 3), and thesource terminal is bonded also to a wire 51. The second diode elementDi2 has a cathode terminal at its lower surface (−Z direction-sidesurface) facing the second lower conductor layer 43, and has an anodeterminal at its upper surface (+Z direction-side surface) of an oppositeside to the second lower conductor layer 43. Therefore, the cathodeterminal is bonded to the second lower conductor layer 43 by thehigh-temperature solder 97A. To the anode terminal, a wire 46 is bonded.The high-temperature solder 97A is a solder whose melting point ishigher than that of the medium-temperature solder 95, and belongs to ahigh temperature range of approximately 300° C.

To the second board bonding area 73 set, on a surface (+Z direction-sidesurface) of the second lower conductor layer 43, between the secondterminal bonding area 71 and the second element bonding area 72, thesecond upper board 42 is bonded by a high-temperature solder 97B. Thesecond upper board 42 uses as a base substrate an insulating substratemade of an insulating material such as a ceramic. The second upperconductor layer 44 described above is formed on an upper surface (a +Zdirection-side surface) of the insulating substrate, and on a lowersurface (a −Z direction-side surface) thereof, a bonding conductor layer54 is formed. The bonding conductor layer 54 is made of, for example, acopper foil formed on the surface of the second upper board 42. Thebonding conductor layer 54 is bonded to the second lower conductor layer43 via the high-temperature solder 97B. The high-temperature solder 97Bis the same solder as the high-temperature solder 97A.

At a −X direction-side marginal portion of the second upper conductorlayer 44, the second power supply terminal N is bonded by alow-temperature solder 96B. The low-temperature solder 96B is the samesolder as the low-temperature solder 96A.

When the second switching element Tr2 conducts, a current that hasflowed in from the output terminal OUT flows in the +X direction throughthe second lower conductor layer 43, and reaches the second switchingelement Tr2. The current that has flowed through the second switchingelement Tr2 is turned back, flows in the −X direction through the wire45, and reaches the second upper conductor layer 44. Inside the secondupper conductor layer 44, a current flows in the −X direction toward thesecond power supply terminal N. A current flow at this time is shown inFIG. 5B.

On the other hand, when a reverse-direction voltage is applied with thesecond switching element Tr2 cut off, a current in the +X direction thatleads to the second diode element Di2 flows through the wire 46. Thecurrent that has flowed through the second diode element Di2 is turnedback, and flows in the −X direction through the second lower conductorlayer 43.

Thus, a current to flow in the second switching element Tr2 flows in the+X direction and a current from the second switching element Tr2 flowsin the −X direction, so that the current directions are reverse to eachother. In addition, the second lower conductor layer 43 that provides apath of the current to flow in the +X direction and the wire 45 and thesecond upper conductor layer 44 that provide a path of the current toflow in the −X direction are close to each other. Similarly, a currentto flow in the second diode element Di2 flows in the +X direction and acurrent from the second diode element Di2 flows in the −X direction, sothat the current directions are reverse to each other. In addition, thewire 46 and the second upper conductor layer 44 that provide a path ofthe current to flow in the +X direction and the second lower conductorlayer 43 that provides a path of the current to flow in the −X directionare close to each other. That is, the paths of currents that flow inreverse directions to each other are arranged closely. Accordingly, aself-inductance of the second lower conductor layer 43 andself-inductances of the wire 45, 46 and the second upper conductor layer44 are at least partially cancelled out by mutual inductancestherebetween. Accordingly, the inductance of the power module 1 can bereduced.

Next, one example of a preparation method of the power module 1 will beoutlined. By executing the following procedures 1 to 7 in order, a powermodule 1 is prepared.

Procedure 1: Bond the first switching element Tr1, the first diodeelement Di1, and the first upper board 22 to the first lower board 21 bythe high-temperature solders 87A, 87B. Similarly, bond the secondswitching element Tr2, the second diode element Di2, and the secondupper board 42 to the second lower board 41 by the high-temperaturesolders 97A, 97B.

Procedure 2: Bond the first and second lower boards 21, 41 to thesurface of the heat radiating base 2 by the medium-temperature solders85, 95.

Procedure 3: Bond terminals to predetermined positions by alow-temperature solder. The terminals include the first power supplyterminal P, the second power supply terminal N, the output terminal OUT,the connecting member 38, the gate terminals G1, G2, and the sourcesense terminals SS1, SS2. The low-temperature solder may be, forexample, a eutectic tin-lead solder.

Procedure 4: Bond the frame portion 4 of the case 3 to the surface ofthe heat radiating base 2. For bonding, for example, a thermosettingadhesive such as a silicone adhesive may be used. For example, asilicone adhesive can be set by heating at a temperature ofapproximately 150° C. for approximately 1 hour. This temperature islower than the melting points of the solders, and lower than thetemperature of a constituent material (for example, PPS) of the frameportion 4.

Procedure 5: Arrange a gel material (not shown) made of an insulatingmaterial inside the frame portion 4. For example, a silicon gel can beused. The gel material has a function of filling up gaps such as betweenwires, and maintaining an insulated condition therebetween. Therefore,it is preferable to fill the gel material inside the frame 4 up to atleast a position higher than the loop heights of all wires.

Procedure 6: Fix the top plate 5 to the frame portion 4. The fixationmay be performed using an adhesive, or may be performed by screwing. Forfixing the top plate 5, insert the terminals P, N, OUT through theslit-shaped insertion holes 5P, 5N, 5OUT (refer to FIG. 1) formed in thetop plate 5, and insert the gate terminals G1, G2 and the source senseterminals SS1, SS2 through insertion holes 5 a, 5 b, 5 c, 5 d (refer toFIG. 1).

Procedure 7: Bend down the terminals P, N, OUT into prone positions toextend along the upper surfaces of the terminal blocks 15P, 15N, 15OUT.

FIG. 6A is an illustrative side view for explaining a holding structureof the gate terminals G1, G2 and the source sense terminals SS1, SS2,and shows a state with the +X direction-side side plate 6 (refer toFIG. 1) removed. Because the gate terminals G1, G2 and the source senseterminals SS1, SS2 are the same in structure, the holding structure ofthe gate terminals G1, G2 will be described.

The gate terminal G1, G2 has a bonding portion 101, a first risingportion 102, a transverse portion 103, and a second rising portion 104.The bonding portion 101 is solder-bonded to the controlling conductorlayer 28, 48, and is formed in a plate shape parallel to the principalsurface of the lower board 21, 41. The first rising portion 102 isjoined to one edge portion of the bonding portion 101, rises in adirection (+Z direction) to separate from the lower board 21, 41, and isformed in an L-shape in section. The transverse portion 103 is joined toan upper end of the first rising portion 102, and extends in a direction(in this embodiment, the Y direction) parallel to the principal surfaceof the lower board 21, 41. The traverse portion 103 is formed in anL-shape in section in a region from its base end portion on the firstrising portion 102 side up to the length of a predetermined length. Thatis, the transverse portion 103 has a first plate-shaped portion 103 aformed in a band shape parallel to the principal surface of the lowerboard 21, 41 and a band-shaped second plate-shaped portion 103 b risingin the +Z direction from one side edge (in this embodiment, a −Xdirection-side side edge) of the first plate-shaped portion 103 a. Thesecond plate-shaped portion 103 b is formed shorter than the firstplate-shaped portion 103 a. The second plate-shaped portion 103 b risesin a direction (+Z direction) to separate from the lower board 21, 41,and its upper end edge (+Z direction-side end edge) is formed parallelto the principal surface of the lower board 21, 41. The second risingportion 104 is joined to a front end portion of the transverse portion103. The second rising portion 104 is made of a plate-shaped body risingin a direction (+Z direction) to separate from the lower board 21, 41,and has a wide-width main body portion 104 a and a narrow width portion104 b linked with an upper end edge (a +Z direction-side end edge) ofthe main body portion 104 a. Accordingly, in a joining portion betweenthe main body portion 104 a and the narrow width portion 104 b, a pairof shoulders 104 c are formed on both sides of the narrow width portion104 b. The narrow width portion 104 b provides an external wiringconnecting portion, and has a hole for making wiring connection easy inits substantially central portion.

The second rising portion 104 is inserted through the insertion hole 5a, 5 b (refer to FIG. 1) formed in the top plate 5 of the case 3.Accordingly, an upper end portion of the main body portion 104 a and thenarrow width portion 104 b are located above (+Z direction) an uppersurface of the top plate 5. The source sense terminals SS1, SS2 are alsosimilarly configured, and are inserted through the insertion holes 5 c,5 d (refer to FIG. 1) formed in the top plate 5 to project in the +Zdirection from the upper surface of the top plate 5.

Below the second rising portion 104, a pedestal 110 (terminal pedestal)is arranged inside the case 3. The pedestal 110 may be made of a resinmaterial (for example, the same material as that of the case 3). Thepedestal 110 may be fixed to an inside surface of the frame portion 4(for example, the end plate 8, 9) of the case 3, or may be fixed to thesurface (+Z direction-side surface) of the heat radiating base 2. Thepedestal 110 is formed in, for example, a rectangular parallelepipedshape, and its upper surface (+Z direction-side surface) that issubstantially flush (that is, substantially the same height) with alower surface of the transverse portion 103 is in contact with or inproximity to the lower surface. On the upper surface of the pedestal110, a partition wall 110 a may be provided in a standing conditionbetween the gate terminal G1, G2 and the source sense terminal SS1, SS2.

On the other hand, a lower surface 111 of the top plate 5 of the case 3is formed substantially flush (that is, substantially the same height)with the upper end edge of the second plate-shaped portion 103 b of thetransverse portion 103. Accordingly, the lower surface 111 is in contactwith or in proximity to the upper end edge of the transverse portion103, and has a function as a terminal retainer that restricts thetransverse portion 103 from moving upward (+Z direction). In FIG. 6A,shown is an example where a minute clearance 112 is formed between thelower surface 111 of the top plate 5 and the upper end edge of thetransverse portion 103 in consideration of dimensional tolerances of thegate terminals G1, G2, the top plate 5, etc.

Due to such a structure, the gate terminals G1, G2 are reliably held.That is, in the case of connection or removal of wiring and the likewith respect to the gate terminals G1, G2, external force is applied tothe gate terminals G1, G2. At this time, a push-in force applieddownward (−Z direction) to the second rising portion 104 is received bythe pedestal 110, and a pull-out force applied upward (+Z direction) tothe second rising portion 104 is received by the lower surface 111 ofthe top plate 5. Accordingly, displacement in the Z direction ordeformation of the gate terminals G1, G2 can be prevented, and further,application of an external force applied to the gate terminals G1, G2can be inhibited or prevented from being applied to the bonding portion101. Accordingly, connection reliability of the gate terminals G1, G2can be improved. For the same reason, connection reliability can beimproved also for the source sense terminals SS1, SS2. Therefore, thepower module 1 has sufficient reliability, and thus has sufficientdurability.

FIG. 6B is an illustrative side view for explaining another example of aholding structure of the gate terminals G1, G2 and the source senseterminals SS1, SS2, and shows a state with the +X direction-side sideplate 6 (refer to FIG. 1) removed. In FIG. 6B, corresponding parts ofthe parts of FIG. 6A described above are denoted by the same referencesigns as in FIG. 6A.

In this structure example, the lower surface 111 of the top plate 5 isnot substantially flush with the upper end edge of the transverseportion 103. In the position corresponding to a position above (+Zdirection) the transverse portion 103, a terminal retainer 113 isprovided at the lower surface 111 of the top plate 5. The terminalretainer 113 projects downward (−Z direction) from the lower surface 111of the top plate 5, has at its lower surface a restriction surface 113Athat is parallel to the transverse portion 103. The restriction surface113A is formed substantially flush (that is, substantially the sameheight) with the transverse portion 103. Accordingly, the restrictionsurface 113A is in contact with or in proximity to the upper end edge ofthe transverse portion 103, and restricts the transverse portion 103from moving upward (+Z direction). Also by such a structure, the sameadvantageous effects as those of the structure of FIG. 6A can berealized. In FIG. 6B, shown is an example where a minute clearance 114is formed between the restriction surface 113A and the upper end edge ofthe transverse portion 103 in consideration of dimensional tolerances ofthe gate terminals G1, G2, the top plate 5, the terminal retainer 113,etc.

FIG. 7A is a view for explaining an effect of reducing inductance by areduction in the length of wires. In FIG. 7A, shown are calculationexamples in which signals of a frequency of 1 MHz are input to aluminumwires with a diameter of 350 nm to determine inductance. Curve L1 showsa result of inductance measured for single wires of various lengths.Curve L2 shows a result of inductance measured for two parallel wires ofvarious lengths. Curve L3 shows a result of inductance measured forthree parallel wires of various lengths.

It can be understood from curves L1 to L3 that the larger the number ofwires, the more inductance is reduced, and the shorter the wire length,the more inductance is reduced. Further, it can be understood fromcurves L1 to L3 that a reduction in the wire length is more effectivefor a reduction in inductance than an increase in the number of wires.

FIG. 7B is a view for explaining an effect of reducing inductance by anincrease in the entire arrangement width of wires. In FIG. 7B, shown arecalculation examples in which signals of a frequency of 1 MHz are inputto aluminum wires with a diameter of 350 nm and a length of 20 mm todetermine inductance. Curve L11 shows a result of inductance calculatedby variously setting the interval (entire arrangement width) of twoparallel wires. Curve L12 shows a result of inductance calculated byarranging in parallel three wires at equal intervals with variously setentire arrangement widths. Curve L13 shows a result of inductancecalculated by arranging in parallel six wires at equal intervals withvariously set entire arrangement widths.

It can be understood from curves L11 to L13 that the larger the entirearrangement width, the more advantageous for a reduction in inductance.Moreover, it can be understood by a comparison of curves L11 to L13 thatan increase in the entire arrangement width is more effective for areduction in inductance than an increase in the number of wires.

As in the above, according to the first embodiment, the current path inthe first board assembly 20 that forms an upper arm circuit 81 flowsfrom the first power supply terminal P toward the first switchingelement Tr1, and is turned back by the first switching element to leadto the first upper conductor layer 24. The current path is thus turnedback, and moreover, the first lower conductor layer 23 and ‘the wire 25and the first upper conductor layer 24’ that form a pair of currentpaths where currents flow in reverse directions to each other are closeto each other. Accordingly, the inductance is reduced. Further, thefirst switching elements Tr1 and the first upper conductor layer 24 areconnected therebetween by a plurality of wires 25 arranged along pathsto have the minimum lengths, respectively. Accordingly, the inductanceis further reduced. In addition, the wires 25 are routed so as to havean entire arrangement width extending substantially the entire width ofone side (a side at the X direction side) of the first upper conductorlayer 24. The wires 26 that connect the diode elements Di1 and the firstupper conductor layer 24 are also arranged so as to have an entirearrangement width extending substantially the entire width of one side(a side at the X direction side) of the first upper conductor layer 24.Accordingly, the inductance is still further reduced. For the secondboard assembly 40 that forms a lower arm circuit 82, the inductance isreduced in the same manner. Therefore, the power module 1 as a whole hasa small inductance. As a result, loss is reduced by using high-speedswitching-type switching elements Tr1, Tr2 made of SiC semiconductordevices, while a surge voltage is reduced to increase the margin ofbreakdown voltage concurrently.

Second Embodiment

FIG. 8 is a perspective view showing an external appearance of a powermodule according to a second embodiment of this invention. In FIG. 8,corresponding parts of the parts shown in FIG. 1 etc., described aboveare shown with the same reference signs.

The power module 120 includes a case 123 having a substantiallyrectangular parallelepiped shape. The case 123, in this embodiment,surrounds a side surface of the heat radiating base 2. The case 123 isformed of a resin material. As the resin material, particularly, it ispreferable that a heat resistant resin such as PPS (polyphenylenesulfide) is applied. The case 123 shows a rectangular shapesubstantially in alignment with the heat radiating base 2 in a planview, and includes a frame portion 124 fixed to one surface (a +Zdirection-side surface) of the heat radiating base 2 and a top plate 125fixed to the frame portion 124. The top plate 125 blocks one side (a +Zdirection side) of the frame portion 124, and faces the principalsurface of the heat radiating base 2 that blocks the other side (a −Zdirection side) of the frame portion 124. Accordingly, the heatradiating base 2, the frame portion 124, and the top plate 125 define acircuit housing space inside of the case 123.

The frame portion 124 includes a pair of side plates 126, 127 (firstcase components) and a pair of end plates 128, 129 (second casecomponents) that join both ends of the paired side plates 126, 127,respectively. The end plates 128, 129, in the vicinity of theirrespective intermediate portions, have recess portions 130, 131 that arerecessed inward. At bottom surfaces of the recess portions 130, 131,mounting holes 132 that penetrate therethrough in the Z direction areformed. The power module 120 is, by a bolt (not shown) inserted throughthe mounting hole 132 and the corresponding mounting hole 12 (refer toFIG. 9) of the heat radiating base 2, fixed to a predetermined fixingposition of a mounting target. A heat sink or other cooling means may bemounted by using the mounting hole 132. Recess portions 133, 134 areformed in the vicinity of intermediate portions of a pair of end sidesof the top plate 125 so as to be in alignment with the recess portions130, 131 of the end plates 128, 129.

On one side plate 126 (a +X direction-side side plate), a terminal block15OUT for an output terminal OUT is formed projecting outward (+Xdirection) to separate from a principal surface of the side plate 126.The terminal block 15OUT has a substantially rectangular shape, and atits upper surface, a rectangular-shaped depression that forms areceiving portion 143 (refer to FIG. 11) to receive a front end portionof the output terminal OUT is formed. The front end portion of theoutput terminal OUT is led out of the case 123 along the X direction viaa slit-shaped insertion hole 140 formed in the side plate 126, and isarranged at the receiving portion 143 of the terminal block 15OUT.

On the other side plate 127 (a −X direction-side side plate), a pair ofterminal blocks 15P, 15N are formed projecting outward (−X direction) toseparate from a principal surface of the side plate 127. The terminalblocks 15P, 15N have substantially rectangular shapes. At an uppersurface of the terminal block 15P, a depression that forms a receivingportion 144 (refer to FIG. 11) to receive a front end portion of thefirst power supply terminal P is formed. Similarly, at an upper surfaceof the terminal block 15N, a depression that forms a receiving portion145 (refer to FIG. 11) to receive a front end portion of the secondpower supply terminal N is formed. The first power supply terminal P isled out of the case 123 along the −X direction via a slit-shapedinsertion hole 141 (refer to FIG. 11) extending linearly in thelongitudinal direction (Y direction) of the side plate 127, and isarranged at the receiving portion 144 of the terminal block 15P.Similarly, the second power supply terminal N is led out of the case 123along the −X direction via a slit-shaped insertion hole 142 (refer toFIG. 11) extending linearly in the longitudinal direction (Y direction)of the side plate 127, and is arranged at the receiving portion 145 ofthe terminal block 15N.

The terminal blocks 15OUT, 15P, 15N are each provided with a hexagonalcylinder-shaped recess portion (not shown) opened in substantially thecenter. Nuts 146, 147, 148 (refer to FIG. 11) are embedded and fixed tothe hexagonal cylinder-shaped recess portions, respectively. Theterminals OUT, P, N are connected to a bus bar (not shown) provided onthe mounting target side by using bolts (not shown) that are screwedinto the nuts 146, 147, 148.

FIG. 9 is an illustrative perspective view for explaining aconfiguration of a power module circuit housed inside the case 123, andFIG. 10 is a plan view thereof. In FIG. 9 and FIG. 10, correspondingparts of the parts shown in FIG. 2 and FIG. 3 described above aredenoted with the same reference signs.

Also in this embodiment, a first board assembly 20 and a second boardassembly 40 are loaded on one surface (a +Z direction-side surface) ofthe heat radiating base 2. However, in the first embodiment describedabove, an interconnection between the first and second board assemblies20, 40 is achieved by the connecting member 38, while in the secondembodiment, the output terminal OUT takes charge of an interconnectionbetween the first and second board assemblies 20, 40.

When described more specifically, the output terminal OUT is, in thisembodiment, made of a band-shaped plate-like body arranged, along aboundary portion between the first and second board assemblies 20, 40,parallel to the principal surface of the heat radiating base 2. That is,the output terminal OUT includes a main body portion 150 made of aband-shaped plate-like body extending along the X direction, a first legportion 151 drooping from one side edge of a base end portion (a −Xdirection-side end portion) of the main body portion 150 and bonded tothe first upper conductor layer 24, and a second leg portion 152drooping from the other side edge of the base end portion and connectedto the second lower conductor layer 43. The main body portion 150extends linearly along the X direction, and is formed entirely with asubstantially uniform width, and its front end portion is led out ontothe terminal block 15OUT outside of the case 123 after being insertedthrough the side plate 126. The first leg portion 151 has a droopingportion 151 a drooping from the main body portion 150 and a bondingportion 151 b bent from a lower edge (a −Z direction-side edge) of thedrooping portion 151 a toward inside (+Y direction) of the first upperconductor layer 24, and the bonding portion 151 b is bonded to a −Ydirection-side marginal portion of the first upper conductor layer 24.The drooping portion 151 a is made of a band-shaped plate-like bodyalong a plane (an X-Z plane) including the X direction and the Zdirection. The bonding portion 151 b is made of a band-shaped plate-likebody parallel to the principal surface of the heat radiating base 2, andis formed with the same width as that of the drooping portion 151 a. Thesecond leg portion 152 has a drooping portion 152 a drooping from themain body portion 150 and a bonding portion 152 b bent from a lower edgeof the drooping portion 152 a toward inside (−Y direction) of the secondlower conductor layer 43, and the bonding portion 152 b is bonded to a+Y direction-side marginal portion of the second lower conductor layer43. The drooping portion 152 a is made of a band-shaped plate-like bodyalong a plane (an X-Z plane) including the X direction and the Zdirection. The bonding portion 152 b is made of a band-shaped plate-likebody parallel to the principal surface of the heat radiating base 2, andis formed with the same width as that of the drooping portion 152 a.Therefore, the first upper conductor layer 24 and the second lowerconductor layer 43 are connected with the minimum path length via a baseend-side part of the main body portion 150 and the first and second legportions 151, 152. The first upper conductor layer 24 and the secondterminal bonding area 71 of the second lower conductor layer 43 aremisaligned in the X direction, and thus accordingly, the first andsecond leg portions 151, 152 are also formed at positions misaligned inthe X direction.

The first power supply terminal P has a main body portion 155 made of aband-shaped plate-like body parallel to the principal surface of theheat radiating base 2 and a leg portion 156 drooping from one end (an Xdirection end) of the main body portion 155 and bonded to the firstterminal bonding area 61 of the first lower conductor layer 23. The mainbody portion 155 extends backward (−X direction) along the principalsurface of the heat radiating base 2, and is led out onto the terminalblock 15P outside of the case 123 after being inserted through the sideplate 127. The leg portion 156 is formed by bending a band-shapedplate-like body narrower in width than the main body portion 155. Thatis, the leg portion 156 has a drooping portion 156 a drooping from themain body portion 155 and a bonding portion 156 b bent from a lower endedge (a −Z direction-side edge) of the drooping portion 156 a in the +Xdirection, and the bonding portion 156 b is bonded to the first terminalbonding area 61 of the first lower conductor layer 23. The droopingportion 156 a is made of a band-shaped plate-like body along a plane (aY-Z plane) including the Y direction and the Z direction. The bondingportion 156 b is made of a band-shaped plate-like body parallel to theprincipal surface of the heat radiating base 2, and is formed with thesame width as that of the drooping portion 156 a.

The second power supply terminal N has a main body portion 159 made of aband-shaped plate-like body parallel to the principal surface of theheat radiating base 2 and a leg portion 160 drooping from one end (an Xdirection end) of the main body portion 159 and bonded to the secondupper conductor layer 44. The main body portion 159 extends backward (−Xdirection) along the principal surface of the heat radiating base 2, andis led out onto the terminal block 15N outside of the case 123 afterbeing inserted through the side plate 127. The leg portion 160 is formedby bending a band-shaped plate-like body narrower in width than the mainbody portion 159. That is, the leg portion 160 has a drooping portion160 a drooping from the main body portion 159 and a bonding portion 160b bent from a lower edge of the drooping portion 160 a in the +Xdirection, and the bonding portion 160 b is bonded to the second upperconductor layer 44. The drooping portion 160 a is made of a band-shapedplate-like body along a plane (a Y-Z plane) including the Y directionand the Z direction. The bonding portion 160 b is made of a band-shapedplate-like body parallel to the principal surface of the heat radiatingbase 2, and is formed with the same width as that of the droopingportion 160 a.

By such a configuration, a lateral lead-out terminal-type power module120 whose terminals P, N, OUT are led out in the directions parallel tothe principal surfaces of the heat radiating base 2 and the first lowerboard 21 and the second lower board 41 can be provided. Moreover,because the lengths of the first and second power supply terminals P, Ncan be reduced, the self-inductances of the terminals P, N can bereduced. As a result, the power module 120 has a further reducedinductance, and thus a surge voltage can be reduced to improve themargin of breakdown voltage concurrently. With regard to thisconfiguration, an inductance calculated for the upper arm circuit 81(first board assembly 20) in response to a signal of a frequency of 1MHz was 18.8 nH.

Because the terminals P, N, OUT are led out laterally, for example, acontrol board to control the switching elements Tr1, Tr2 can be arrangedat an upper surface side of the case 123. Accordingly, a power moduleincluding also the control board can be downsized.

In addition, the electrical configuration of the power module 120according to the second embodiment is the same as that of the firstembodiment described above, and as shown in FIG. 4. The current paths inthe first and second board assemblies 20, 40 (the upper arm circuit 81and lower arm circuit 82) are also the same as those of the firstembodiment, and as shown in FIG. 5. Therefore, in the same manner as inthe first embodiment, the current paths where currents flow in reversedirections to each other are close to each other in the first and secondboard assemblies 20, 40, and accordingly, an effect to cancel outinductances can be obtained.

FIG. 11 is an exploded perspective view of the case 123. In thisembodiment, the side plates 126, 127 are attached to both end portionsof the end plates 128, 129 by pluralities of bolts 135, 136. That is, inthe side plates 126, 127, a plurality of bolt insertion holes 126 a, 127a are formed in the vicinity of both longitudinal (Y direction) endedges, respectively. In both end surfaces of the end plates 128, 129, aplurality of screw holes 137 corresponding to the bolt insertion holes126 a and a plurality of screw holes 138 corresponding to the boltinsertion holes 127 a are formed. The bolts 135 are fitted by screwinginto the screw holes 137 after being inserted through the bolt insertionholes 126 a. Accordingly, the side plate 126 is attached to the endplates 128, 129. The bolts 136 are fitted by screwing into the screwholes 138 after being inserted through the bolt insertion holes 127 a.Accordingly, the side plate 127 is attached to the end plates 128, 129,and thus a frame portion 124 made of an assembly of a pair of sideplates 126, 127 and a pair of end plates 128, 129 is assembled. Further,as a result of a top plate 125 being fixed to the frame portion 124 byan adhesive (for example, a thermosetting adhesive), a case 123 isassembled.

In the second embodiment, the terminals P, N, OUT are lead out laterallyafter being inserted through the side plates 126, 127. For this reason,the frame portion 124 cannot be assembled in advance before bonding theterminals P, N, OUT to the first and second board assemblies 20, 40.Therefore, the terminals P, N, OUT are soldered and bonded to the firstand second board assemblies 20, 40, and then the frame portion 124 isassembled. After the terminals P, N, OUT are bonded to the first andsecond board assemblies 20, 40, the pair of end plates 128, 129 areadhered to both end portions (Y direction both end portions) of the heatradiating base 2 by use of an adhesive (for example, a thermosettingadhesive). Next, the side plate 126 is made to approach the heatradiating base 2 from the +X direction, the output terminal OUT isinserted through the slit-shaped insertion hole 140, and then the sideplate 126 is fixed to the end plates 128, 129 by the bolts 135. Further,the side plate 127 is made to approach the heat radiating base 2 fromthe −X direction, the first and second power supply terminals P, N areinserted through the slit-shaped insertion holes 141, 142, respectively,and then the side plate 127 is fixed to the end plates 128, 129 by thebolts 136. Thereafter, a gel material (not shown. For example, a silicongel) to maintain insulation between wires is arranged inside the frameportion 124. Then, the top plate 125 is adhered to the frame portion124, so that the case 123 is sealed. Thereafter, a heating treatment toset the adhesive may be performed as necessary.

In order to realize a lateral lead-out terminal-type power module, itmay be considered to integrate in advance the terminals P, N, OUT intothe frame portion 124 by insert molding. In this case, the frame portion124 is not necessarily be an assembly, and can be formed of anintegrally molded piece. However, if such a configuration is adopted,the frame portion 124 and an adhesive to adhere the frame portion 124 tothe heat radiating base 2 must withstand a high temperature when theterminals P, N, OUT is soldered. For this reason, it becomes difficultto select the material of the frame portion 124 and select an adhesive.Therefore, as described above, it is preferable to provide the frameportion 124 as an assembly, and fix the frame portion 124 to the heatradiating base 2 after solder bonding of the terminals P, N, OUT.

In addition, preparation of the first and second board assemblies 20,40, mounting of these onto the heat radiating base 2, and bonding of theterminals P, N, OUT can be performed by the same procedures (procedures1 to 3 described above) as in the case of the first embodiment describedabove.

Also in the second embodiment, the same structure as in the firstembodiment described above is adopted for stable holding of the gateterminals G1, G2 and the source sense terminals SS1, SS2 (refer to FIG.6A and FIG. 6B). However, in the second embodiment, pedestals 110 arefixed to X direction-side end portions of the end plates 128, 129. Thepedestals 110 may be integrally molded with the end plates 128, 129.

[Terminal Variations]

FIG. 12 to FIG. 30 are perspective views for explaining variousvariations of the terminals P, N, OUT. In these figures, correspondingparts of the parts shown in FIG. 1 to FIG. 11 described above aredenoted by the same reference signs.

In a configuration example of FIG. 12, the terminals P, N, OUT are ledout to one side (−X direction) parallel to the principal surface of theheat radiating base 2. The output terminal OUT is arranged closer to the−Y direction than the second power supply terminal N, and has aconnecting portion 161 bonded to the first upper conductor layer 24after passing below the second power supply terminal N (−Z directionside. Second lower board 41 side). The connecting portion 161 connectsthe first upper conductor layer 24 and the second lower conductor layer43. The leg portion 156 of the first power supply terminal P is formedwith a width substantially equal to that of the main body portion 155,and similarly, the leg portion 160 of the second power supply terminal Nis formed with a width substantially equal to that of its main bodyportion 159. In this configuration, the lengths of not only the firstand second power supply terminals P, N but also the output terminal OUTare reduced, and thus the inductance can be further reduced. With regardto this configuration, an inductance calculated for the upper armcircuit 81 (first board assembly 20) in response to a signal of afrequency of 1 MHz was 18.13 nH.

In a configuration example of FIG. 13, the output terminal OUT isarranged between the first and second power supply terminals P, N, andthis configuration example is similar to the second embodiment describedabove. However, the output terminal OUT is, together with the first andsecond power supply terminals P, N, led out to one side (−X direction)parallel to the principal surface of the heat radiating base 2. However,the main body portion 150 of the output terminal OUT is formed with anarrow width at its base end side. Accordingly, the connection pathlength of an interconnection between the first and second boardassemblies 20, 40 via the output terminal OUT is reduced. The legportion 156 of the first power supply terminal P is formed with a widthsubstantially equal to that of the main body portion 155, and similarly,the leg portion 160 of the second power supply terminal N is formed witha width substantially equal to that of its main body portion 159. Inthis configuration, the lengths of the terminals P, N, OUT areshortened, and further the interconnection path length between the firstand second board assemblies 20, 40 is reduced, and thus the inductanceis reduced accordingly. Additionally, the path of a current that flowsin from the power supply terminal P and flows out to the output terminalOUT and the path of a current that flows in from the output terminal OUTand flows out from the power supply terminal N do not cross each otherwithin the output terminal OUT. Also whereby, the inductance can bereduced. With regard to this configuration, an inductance calculated forthe upper arm circuit 81 (first board assembly 20) in response to asignal of a frequency of 1 MHz was 20.17 nH.

In a configuration example of FIG. 14, the first and second power supplyterminals P, N and the output terminal OUT are all led out in directionsparallel to the principal surface of the heat radiating base 2, andfurther, the first and second power supply terminals P, N overlap eachother across a minute distance from each other. More specifically, theoutput terminal OUT includes a main body portion 150 extending in the Xdirection along a boundary region between the first and second boardassemblies 20, 40. The main body portion 150 is a band-shaped plate-likebody parallel to the principal surface of the heat radiating base 2, andits front end portion (a +X direction-side end portion) is led out inthe +X direction. Moreover, the main body portion 150 is formed with anarrower width at the majority of the region to be housed inside thecase than that of its connection end to be led out outside the case. Ina base end portion (a −X direction-side end portion) of the main bodyportion 150, a leg portion 151 bonded to the first upper conductor layer24 is formed at one side edge (a +Y direction-side side edge). At theother side edge (a −Y direction-side side edge) of the base end portion,a leg portion 152 bonded to the second lower conductor layer 43 isformed.

The first power supply terminal P has a main body portion 173 arrangedbehind (−X direction side) the main body portion 150 of the outputterminal OUT. The main body portion 173 extends in the X direction, andits front end portion (−X direction-side end portion) is led out in the−X direction. The main body portion 173 is formed of a band-shapedplate-like body parallel to the principal surface of the heat radiatingbase 2. On a base end portion side (a +X direction-side end portion) ofthe main body portion 173, a transverse portion 174 extending in the +Ydirection toward the first board assembly 20 side is formed. Thetransverse portion 174 is formed of a band-shaped plate-like bodyparallel to the principal surface of the heat radiating base 2. At afront end edge (a +Y direction-side end edge) of the transverse portion174, a leg portion 175 drooping toward the heat radiating base 2 andbonded to the first terminal bonding area 61 of the first lowerconductor layer 23 is formed. The leg portion 175 is formed by bending aband-shaped plate-like body into an L-shape, and has a drooping portion175 a extending in the Z direction, and a bonding portion 175 bextending in the +Y direction from a lower end (a −Z direction-side end)of the drooping portion 175 a. The bonding portion 175 b is bonded tothe first terminal bonding area 61. The drooping portion 175 a is madeof a plate-like body parallel to a plane (an X-Z plane) along the Xdirection and the Z direction, and the bonding portion 175 b is made ofa plate-like body parallel to the principal surface of the heatradiating base 2.

The second power supply terminal N has a main body portion 176 arranged,behind (−X direction side) the main body portion 150 of the outputterminal OUT, with a minute interval (for example, 1 mm) kept above thefirst power supply terminal P. The main body portion 176 extends in theX direction, and its front end portion (−X direction-side end portion)is led out in the −X direction. The main body portion 176 is formed of aband-shaped plate-like body parallel to the principal surface of theheat radiating base 2. The majority (approximately 75% level) of theregion at a front end portion side (a −X direction side) in the mainbody portion 176 overlaps the main body portion 173 of the first powersupply terminal P. More specifically, the main body portions 173, 176 ofthe first and second power supply terminals P, N have substantiallyequal widths (widths in the Y direction. For example, 6 mm), areparallel to each other, and face each other with a minute interval keptin the Z direction. The main body portions 173, 176 are led out towardthe −X direction up to substantially the same positions in a plan view.

A base end portion (a +X direction-side end portion) of the main bodyportion 176 extends in the +X direction beyond the main body portion 173of the first power supply terminal P. To the base end portion, atransverse portion 177 extending in the −Y direction toward the secondboard assembly 40 side is joined. The transverse portion 177 is formedof a band-shaped plate-like body parallel to the principal surface ofthe heat radiating base 2. At a front end edge (a −Y direction-side endedge) of the transverse portion 177, a leg portion 178 drooping towardthe heat radiating base 2 and bonded to the second upper conductor layer44 is formed. The leg portion 178 is formed by bending a band-shapedplate-like body into an L-shape, and has a drooping portion 178 aextending in the Z direction, and a bonding portion 178 b extending inthe −Y direction from a lower end (a −Z direction-side end) of thedrooping portion 178 a. The bonding portion 178 b is bonded to thesecond upper conductor layer 44. The drooping portion 178 a is made of aband-shaped plate-like body parallel to a plane (an X-Z plane) along theX direction and the Z direction, and the bonding portion 178 b is madeof a band-shaped plate-like body parallel to the principal surface ofthe heat radiating base 2.

In this configuration example, the first and second power supplyterminals P, N where currents flow in reverse directions to each otheroverlap each other with a minute interval kept therebetween, and thustheir currents cancel out each other's inductance. Accordingly, theinductance can be reduced. Moreover, because the output terminal OUT isformed with a narrow width in the case, the interconnection path lengthbetween the first and second board assemblies 20, 40 is reduced, wherebyalso the inductance is reduced. With regard to this configuration, aninductance calculated for the upper arm circuit 81 (first board assembly20) in response to a signal of a frequency of 1 MHz was 16.6 nH.

A configuration example of FIG. 15 is similar to the configurationexample of FIG. 14. In this configuration example, the widths (widths inthe Y direction) of the first and second power supply terminals P, N areprovided wider (for example, 12 mm) than in the case of theconfiguration example of FIG. 14. The transverse portions 174, 177 areshortened accordingly. With regard to this configuration, an inductancecalculated for the upper arm circuit 81 (first board assembly 20) inresponse to a signal of a frequency of 1 MHz was 14.8 nH. That is, incomparison with the configuration example of FIG. 14, the inductance wasreduced by approximately 1 nH.

A configuration example of FIG. 16 is a variation of the configurationexample of FIG. 15, and the interval between the first and second powersupply terminals P, N (interval in the Z direction) is provided wide(for example, 5 mm) With regard to this configuration, an inductancecalculated for the upper arm circuit 81 (first board assembly 20) inresponse to a signal of a frequency of 1 MHz was 20.8 nH. Therefore, itcould be understood that the narrower the interval between the first andsecond power supply terminals P, N, the more advantageous for areduction in inductance.

A configuration example of FIG. 17 is a variation of the configurationexample of FIG. 15, and only a front end portion (a −X direction-sideend portion) 176 a is lifted in the main body portion 176 of the secondpower supply terminal N. That is, a region at a base end portion side ofthe main body portion 176 of the second power supply terminal N isarranged with a minute interval (for example, 1 mm) kept with respect tothe main body portion 173 of the first power supply terminal P. On theother hand, the front end portion 176 a of the second power supplyterminal N is arranged with a relatively large interval (for example, 5mm) kept with respect to the main body portion 173 of the first powersupply terminal P. This structure has an advantage of making externalconnection (for example, a bus bar connection) to the first and secondpower supply terminals P, N easy. With regard to this configuration, aninductance calculated for the upper arm circuit 81 (first board assembly20) in response to a signal of a frequency of 1 MHz was 15.3 nH.Therefore, it could be understood that an inductance reducing effect canbe obtained by overlapping the first and second power supply terminalsP, N with a minute interval even in a partial region.

A configuration example of FIG. 18 is a variation of the configurationexample of FIG. 17, and a base end portion side (a +X direction side) ofthe second power supply terminal N is cut away to eliminate anoverlapping part with the output terminal OUT. The transverse portion177 has an L-shape that extends in the +X direction from a part closerto the −Y direction of the base end portion of the main body portion 176to reach above the second upper conductor layer 44, and is then bent inthe −Y direction. In this configuration example, the bonding portion 178b of the leg portion 178 is formed wide in width (width in the Xdirection), and is therefore bonded to the second upper conductor layer44 with a large area (footprint). With regard to this configuration, aninductance calculated for the upper arm circuit 81 (first board assembly20) in response to a signal of a frequency of 1 MHz was 14.7 nH. It canbe understood from this result that the inductance can be reduced byreducing an overlapping part between the second power supply terminal Nand the output terminal OUT.

A configuration example of FIG. 19 is a variation of the configurationexample of FIG. 18. In this configuration, a cut 176 b for currentconfinement is formed, in the main body portion 176 of the second powersupply terminal N, at a region facing the main body portion 173 of thefirst power supply terminal P with a minute interval. The cut 176 b islinearly formed along the +Y direction from a side edge on the secondboard assembly 40 side toward the first board assembly 20. Also in themain body portion 173 of the first power supply terminal P, a cut 173 bin the same shape is formed at a position facing the cut 176 b. Due tosuch a configuration, the directions of currents that flow in the firstand second power supply terminals P, N can be approximated to beparallel (to be exact, antiparallel), so that the inductance cancelingeffect can be enhanced. With regard to this configuration, an inductancecalculated for the upper arm circuit 81 (first board assembly 20) inresponse to a signal of a frequency of 1 MHz was 15.3 nH.

A configuration example of FIG. 20 is a variation of the configurationexample of FIG. 18. In this configuration, the transverse portion 177extends in the −Y direction from a side edge of the base end portion ofthe main body portion 176. The leg portion 178 droops from a +Xdirection-side edge portion of the transverse portion 177. That is, thedrooping portion 178 a of the leg portion 178 is formed parallel to aplane (a Y-Z plane) along the Y direction and the Z direction. Thebonding portion 178 b is joined to a lower edge of the drooping portion178 a. The bonding portion 178 b, in this configuration example, has arectangular shape long in the Y direction. With regard to thisconfiguration, an inductance calculated for the upper arm circuit 81(first board assembly 20) in response to a signal of a frequency of 1MHz was 14.7 nH.

A configuration example of FIG. 21 is a variation of the configurationexample of FIG. 17. For this configuration example, the transverseportion 177 of the second power supply terminal N is shortened (morepreferably, eliminated), and at a marginal portion (a +Y direction-sidemarginal portion) of the second upper conductor layer 44 closer to thefirst board assembly 20, the leg portion 178 is bonded to the secondupper conductor layer 44. Accordingly, the current path through thesecond power supply terminal N is shortened, which can thus contributeto a reduction in inductance. With regard to this configuration, aninductance calculated for the upper arm circuit 81 (first board assembly20) in response to a signal of a frequency of 1 MHz was 13.4 nH.

A configuration example of FIG. 22 is a variation of the configurationexample of FIG. 21. For this configuration example, the second powersupply terminal N is moved in the −Y direction, whereby an overlappingregion between the first and second power supply terminals P, N iseliminated. The leg portion 178 of the second power supply terminal Nis, in the vicinity of a marginal portion (a −Y direction-side marginalportion) of the second upper conductor layer 44 of an opposite side tothe first board assembly 20, bonded to the second upper conductor layer44. With regard to this configuration, an inductance calculated for theupper arm circuit 81 (first board assembly 20) in response to a signalof a frequency of 1 MHz was 18.7 nH.

A configuration example of FIG. 23 is a variation of the configurationexample of FIG. 22. For this configuration example, the second powersupply terminal N is provided with a second leg portion 179, in additionto the leg portion 178 described above. The first leg portion 178 isprovided at a −Y direction-side edge portion of the main body portion176, while the second leg portion 179 is provided at a +Y direction-sideedge portion of the main body portion 176. The second leg portion 179includes a drooping portion 179 a drooping from the main body portion176 and a bonding portion 179 b joined to a lower end of the droopingportion 179 a. The drooping portion 179 a is formed of a band-shapedplate-like body parallel to a plane (an X-Z plane) including the Xdirection and the Z direction. The bonding portion 179 b is formed of aband-shaped plate-like body parallel to the principal surface of theheat radiating base 2. The bonding portion 179 b is connected to aregion in the vicinity of a marginal portion closer to the first boardassembly 20 in the second upper conductor layer 44. In thisconfiguration, more current flows to the second leg portion 179 close tothe output terminal OUT, so that the current path length can besubstantially reduced. Accordingly, the inductance is reduced. Withregard to this configuration, an inductance calculated for the upper armcircuit 81 (first board assembly 20) in response to a signal of afrequency of 1 MHz was 15.8 nH.

A configuration example of FIG. 24 is a variation of the configurationexample of FIG. 23. The first power supply terminal P is located furtheron the first board assembly 20 side (+Y direction side) than the outputterminal OUT, and is led out in the −X direction. The power supplyterminal P has a main body portion 180 made of a band-shaped plate-likebody and first and second leg portions 181 and 182 drooping from bothside edges of a base end side (a +X direction side) of the main bodyportion 180 and bonded to the first lower conductor layer 23. The mainbody portion 180 is, at substantially the same height position as thatof the output terminal OUT, arranged parallel to the principal surfaceof the heat radiating base 2. The first and second leg portions 181, 182have drooping portions 181 a, 182 a drooping from side edges of the mainbody portion 180 and bonding portions 181 b, 182 b bent at lower endedges of the drooping portions 181 a, 182 a, respectively. The droopingportions 181 a, 182 a are both made of band-shaped plate-like bodiesformed along a plane (an X-Z plane) parallel to the X direction and theZ direction, are formed parallel to each other, and face each other inthe Y direction. The bonding portions 181 b, 182 b are made ofband-shaped plate bodies parallel to the principal surface of the heatradiating base 2, the bonding portion 181 b extends in the −Y directionfrom the lower end edge of the drooping portion 181 a, and the bondingportion 182 b extends in the +Y direction from a lower end portion ofthe drooping portion 182 a. Therefore, the bonding portion 181 b isbonded in the vicinity of a marginal portion on the second boardassembly 40 side in a −X direction-side marginal portion of the firstlower conductor layer 23, and the bonding portion 182 b is bonded in thevicinity of a marginal portion of an opposite side to the second boardassembly 40 in a +X direction-side marginal portion of the first lowerconductor layer 23. The second power supply terminal N has substantiallythe same configuration as in the case of the configuration example ofFIG. 23, but the first and second leg portions 178, 179 are shorter, andthe main body portion 176 is arranged at substantially the same heightposition as that of the output terminal OUT. The main body portion 176does not have in its front end portion an offset part to the above (+Zdirection), and is in its entirety formed in a flat plate shape parallelto the principal surface of the heat radiating base 2. The main portion150 of the output terminal OUT is formed in a plate-like body with asubstantially uniform width from its base end side to its front endside, and is broader in width than in the case of the configurationexample of FIG. 23. With regard to this configuration, an inductancecalculated for the upper arm circuit 81 (first board assembly 20) inresponse to a signal of a frequency of 1 MHz was 25.1 nH.

A configuration example of FIG. 25 is similar to the configurationexample of FIG. 24, but is different in the structure of connectingportions of the first and second power supply terminals P, N.Specifically, the first power supply terminal P is bonded to the firstlower conductor layer 23 by a single leg portion 185 drooping from abase end edge (an +X direction-side end portion) of the main bodyportion 180. The leg portion 185 has a drooping portion 185 asubstantially the same in width as the main body portion 180 and abonding portion 185 b substantially the same in width as the droopingportion 185 a. The drooping portion 185 a droops in the −Z directionfrom the base end edge of the main body portion 180 toward the firstlower conductor layer 23, and is made of a band-shaped plate-like bodyparallel to a plane (a Y-Z plane) including the Y direction and the Zdirection. The bonding portion 185 b is bent at a right angle from alower end edge (a −Z direction-side end edge) of the drooping portion185 a toward the +X direction, and is made of a band-shaped plate-likebody parallel to the principal surface of the heat radiating base 2. Thebonding portion 185 b is bonded to the first lower conductor layer 23.Therefore, the bonding width is substantially equal to the width of thefirst power supply terminal P. The second power supply terminal N alsohas substantially the same structure. That is, the second power supplyterminal N is bonded to the second upper conductor layer 44 by a singleleg portion 186 drooping from a base end edge (an +X direction-side endportion) of the main body portion 176. The leg portion 186 has adrooping portion 186 a substantially the same in width as the main bodyportion 176 and a bonding portion 186 b substantially the same in widthas the drooping portion 186 a. The drooping portion 186 a droops in the−Z direction from the base end edge of the main body portion 176 towardthe second upper conductor layer 44, and is made of a band-shapedplate-like body parallel to a plane (a Y-Z plane) including the Ydirection and the Z direction. The bonding portion 186 b is bent at aright angle from a lower end edge (a −Z direction-side end edge) of thedrooping portion 186 a toward the +X direction, and is made of aband-shaped plate-like body parallel to the principal surface of theheat radiating base 2. The bonding portion 186 b is bonded to the secondupper conductor layer 44. Therefore, the bonding width is substantiallyequal to the width of the second power supply terminal N. With regard tothis configuration, an inductance calculated for the upper arm circuit81 (first board assembly 20) in response to a signal of a frequency of 1MHz was 22.6 nH.

A configuration example of FIG. 26 approximates the configurationexample of FIG. 21. However, the width of the main body portion 150 ofthe output terminal OUT is increased, and accordingly, the length of thetransverse portion 177 of the second power supply terminal N is slightlylonger than that of the configuration example of FIG. 21. Moreover, thelength of a part where the main body portion 176 of the second powersupply terminal N and the first power supply terminal P overlap with aminute interval (for example, 1 mm) therebetween is shorter than that inthe configuration of FIG. 21. More specifically, in the configurationexample of FIG. 21, the main body portion 176 of the second power supplyterminal N overlaps a region not less than 50% of the main body portion173 of the first power supply terminal P with a minute intervaltherebetween. On the other hand, in the configuration example of FIG.26, the main body portion 176 of the second power supply terminal Noverlaps a region less than 50% (for example, approximately 30%) of themain body portion 173 of the first power supply terminal P with a minuteinterval therebetween. With regard to this configuration, an inductancecalculated for the upper arm circuit 81 (first board assembly 20) inresponse to a signal of a frequency of 1 MHz was 14.4 nH.

A configuration example of FIG. 27 is a variation of the configurationexample of FIG. 26. In this configuration example, the heights of thefirst and second power supply terminals P, N are reduced (reduced by,for example, 2 mm as compared with the configuration example of FIG.26). Therefore, the main body portion 150 of the output terminal OUT hasa low portion 150 a with a lower height at its base end portion side (−Xdirection side), has a high portion 150 b further at a +X direction sidethan the low portion 150 a, and has a step portion 150 c formed betweenthe low portion 150 a and the high portion 150 b. The main body portion173 of the first power supply terminal P is formed with substantiallythe same height as that of the low portion 150 a, and accordingly, thelength of the leg portion 175 (length of the drooping portion 175 a) isshorter than that in the configuration example of FIG. 26. The main bodyportion 176 of the second power supply terminal N has, at its base endside (−X direction side), a region formed with substantially the sameheight as that of the high portion 150 b, and the region overlaps thefirst power supply terminal P with a minute interval (for example, 1 mm)kept therebetween. That is, the step 150 c is substantially equal to asum of the thickness of the main body portion 176 of the second powersupply terminal N and the minute interval. According to thisconfiguration, a lead-out position of the second power supply terminal Ncan be arranged at a position sufficiently lower than a top surface ofthe case 123 (refer to FIG. 8), which is advantageous in securing thestrength (resin stiffness) of the case 123 in the neighborhood of thelead-out position of the second power supply terminal N. Of course, thepower module can be reduced in height concurrently. Further, because thelengths of the leg portions 151, 152, 175, 178 of the terminals P, N,OUT are reduced, the current path lengths can be reduced, and theinductance can be accordingly reduced. With regard to thisconfiguration, an inductance calculated for the upper arm circuit 81(first board assembly 20) in response to a signal of a frequency of 1MHz was 12.0 nH.

A configuration example of FIG. 28 is a variation of the configurationexample of FIG. 26. In this configuration example, the main body portion150 of the output terminal OUT is arranged at a position higher thanthat of the main body portions 173, 176 of the first and second powersupply terminals P, N. Accordingly, the leg portion 175 of the firstpower supply terminal P and the leg portion 178 of the second powersupply terminal N are shortened. The main body portion 150 of the outputterminal OUT is, at its base end portion (−X direction side), locatedabove the main body portion 176 (a lower region facing the first powersupply terminal P with a minute clearance) of the second power supplyterminal N, and overlaps the main body portion 176. Because it is notnecessary for the second power supply terminal N to evade the outputterminal OUT, the length of its transverse portion 177 can be providedas the minimum distance (preferably, zero). Thus, the current pathlengths of the first and second power supply terminals P, N are reduced,so that the inductance can be reduced. With regard to thisconfiguration, an inductance calculated for the upper arm circuit 81(first board assembly 20) in response to a signal of a frequency of 1MHz was 12.8 nH.

A configuration example of FIG. 29 is a variation of the configurationexample of FIG. 25. In this configuration example, the first powersupply terminal P is bonded to the first lower conductor layer 23 by ablock-shaped leg portion 191 drooping from the base end edge (Xdirection-side end portion) of the main body portion 180. The legportion 191 has a rectangular parallelepiped shape substantially thesame in width as the main body portion 180, and a bottom surface of theleg portion 191 is bonded to the first lower conductor layer 23.Therefore, the bonding width is substantially equal to the width of themain body portion 180. The second power supply terminal N also hassubstantially the same structure. That is, the second power supplyterminal N is bonded to the second upper conductor layer 44 by ablock-shaped leg portion 192 drooping from the base end edge (Xdirection-side end portion) of the main body portion 176. The legportion 192 has a rectangular parallelepiped shape substantially thesame in width as the main body portion 176, and a bottom surface of theleg portion 192 is bonded to the second upper conductor layer 44.Therefore, the bonding width is substantially equal to the width of themain body portion 176. With regard to this configuration, an inductancecalculated for the upper arm circuit 81 (first board assembly 20) inresponse to a signal of a frequency of 1 MHz was 17.5 nH.

A configuration example of FIG. 30 is similar to the second embodiment.In this configuration example, the lengths of the leg portions of thefirst and second power supply terminals P, N are provided longer (longerby, for example, 2 mm) than those in the case of the second embodiment.Thereby, it is intended to secure a sufficient clearance with thesurface of a gel material arranged on the first and second boardassemblies 20, 40. With regard to this configuration, an inductancecalculated for the upper arm circuit 81 (first board assembly 20) inresponse to a signal of a frequency of 1 MHz was 24.5 nH.

In the embodiments described above, a description has been given, asexamples of switching elements, of the MOS field-effect transistorsformed of SiC semiconductor devices, but other forms of switchingelements such as IGBTs (Insulated Gate Bipolar Transistors) may beapplied. Also, in the embodiments described above, a description hasbeen given of the examples where switching elements and diode elementsare connected by means of wires, but ribbons that are band-shapedconnecting members having rectangular sections may be used instead.Alternatively, a lead frame may be used instead of using a plurality ofwires. Further, in the embodiments described above, a description hasbeen given of the configurations including switching elements and diodeelements, but this invention can be applied also to a semiconductordevice not including diode elements. Moreover, the semiconductor devicedoes not necessarily constitute a power module.

Third Embodiment

FIG. 31A is a schematic plan view showing an internal structure of apower module according to a third embodiment of the present invention.FIG. 31B is a schematic side view of the internal structure of the powermodule shown in FIG. 31A.

The power module 501 includes a heat radiating base 560 and a case 570.The case 570 is formed of an insulating resin material.

Moreover, the power module 501 includes, for example, an IGBT chip 502which is a semiconductor chip with an IGBT. The IGBT chip 502 is formedin a rectangular shape in a plan view.

Moreover, the power module 501 includes a thin plate-like firstelectrode bar 503 and second electrode bar 504. The first electrode bar503 and the second electrode bar 504 are arranged on an insulating board561 provided on the heat radiating base 560. The first electrode bar 503and the second electrode bar 504 are provided side by side separatedfrom each other. The electrode bars 503, 504 are made of, for example,Cu (copper).

A surface at the collector side of the IGBT chip 502 is bonded to thefirst electrode bar 503 via a conductive adhesive 505 such as a solder.On a surface of the emitter side of the IGBT chip 502, an emitterelectrode 506 is formed.

On the emitter electrode 506, at, for example, a position one-sided tothe second electrode bar 504 side, a resilient member 507 withconductivity is provided. The resilient member 507 is made of, forexample, a ribbon wire of Al (aluminum) or Au (gold). The resilientmember 507, as a result of being formed in a shape whose both ends arefixed to the emitter electrode 506 and whose central portion is floatingup from the emitter electrode 506, is resiliently deformable at itscentral portion. The resilient member 507 in such a shape is formed, bymeans of a wire bonder, by ultrasonic-bonding one end of a ribbon wireto the emitter electrode 506, moving the capillary, and thenultrasonic-bonding the other end of the ribbon wire to another positionon the emitter electrode 506.

Moreover, on the second electrode bar 504, at a position one-sided tothe first electrode bar 503 side, a resilient member 508 having the sameconfiguration as that of the resilient member 507 is provided.

As shown in FIG. 31A, in the power module 501, two each of resilientmembers 507, 508 are provided, but the number of resilient members 507,508 are not particularly limited, and it may be one, and may be three ormore.

Between the IGBT chip 502 and the second electrode bar 504, a frame 509for wiring is stretched. The frame 509 is made of, for example, Cu, andis formed in a thin plate shape extending in the direction in which thefirst electrode bar 503 and the second electrode bar 504 are arrangedside by side. One end portion in the longitudinal direction of the frame509 (hereinafter, simply referred to as “one end portion of the frame509”) is almost parallel to the emitter electrode 506, and is inpressure contact with the resilient members 507 on the emitter electrode506 from above. On the other hand, the other end portion at the oppositeside to one end portion in the longitudinal direction of the frame 509(hereinafter, simply referred to as “the other end portion of the frame509”) is almost parallel to the second electrode bar 504, and is inpressure contact with the resilient members 508 on the second electrodebar 504 from above. The frame 509 is bent between its one end portionand the other end portion, and forms, for example, as shown in FIG. 31B,a substantially crank shape in a side view. The emitter electrode 506and the second electrode bar 504 are electrically connected via theresilient members 507, 508 and the frame 509.

A structure including the IGBT chip 502, the first electrode bar 503,the second electrode bar 504, the resilient members 507, 508, and theframe 509 is housed inside the case 570. In the case 570, screw holes571, 572 are formed at positions facing one end portion and the otherend portion of the frame 509. Moreover, in one end portion and the otherend portion of an upper surface of the frame 509, concavities 509 a, 509b are formed, in a plan view, at positions facing center portions of thescrew holes 571, 572. Into the screw holes 571, 572 of the case 570,pressing screws 510, 511 are fitted by screwing from above the case 570,respectively. Then, front end portions of the pressing screws 510, 511are fitted to the concavities 509 a, 509 b, respectively. Accordingly,the frame 509 is fixed to the case 570. Front ends of the pressingscrews 510, 511 press one end portion and the other end portion of theframe 509, respectively. Accordingly, one end portion and the other endportion of the frame 509 press the resilient members 507, 508,respectively, by pressing forces received from the pressing screws 510,511, respectively, and are reliably connected to the resilient members507, 508, respectively.

As in the above, in the power module 501, the collector-side surface ofthe IGBT chip 502 is bonded to the first electrode bar 503. On theemitter-side surface of the IGBT chip 502, the emitter electrode 506 isformed. The emitter electrode 506 is electrically connected with thesecond electrode bar 504 via the frame 509 for wiring. The frame 509forms a thin plate shape, and has a sectional area larger than that ofbonding wires (for example, thin gold wires). For this reason, byadopting the frame 509, the self-inductance can be reduced more than ina structure for which bonding wires are adopted. As a result, a surgevoltage that occurs at the time of switching (turn-off) of the IGBT canbe reduced.

In addition, between the emitter electrode 506 of the IGBT chip 502 andthe frame 509, the resilient member 507 that is resiliently deformableat its central portion is interposed. A connection between the frame 509and the resilient member 507 is achieved not by soldering but as aresult of the resilient member 507 being pressed to the IGBT chip 502side by the frame 509. Therefore, even if a thermalexpansion/contraction difference occurs between the IGBT chip 502 andthe frame 509, the thermal expansion/contraction difference can beabsorbed by deformation of the resilient member 507 or a relative shiftbetween the frame 509 and the resilient member 507. Thus, separation ofthe frame 509 from the resilient member 507 (IGBT chip 502) can beprevented. Moreover, propagation of a stress caused by a thermalexpansion/contraction difference to the IGBT chip 502 can be prevented,and the occurrence of cracks of the IGBT chip 502 resulting from thepropagation of stress can be prevented.

Therefore, according to the structure of the power module 501, theself-inductance can be reduced, and reliability against heat cycle canbe improved.

Moreover, between the second electrode bar 504 and a part of the frame509 facing the second electrode bar 504, the resilient member 508 thatis resiliently deformable at its central portion is interposed. Aconnection between the frame 509 and the resilient member 508 isachieved not by soldering but as a result of the resilient member 508being pressed to the second electrode bar 504 side by the frame 509.Therefore, even if a thermal expansion/contraction difference occursbetween the frame 509 and the second electrode bar 504, the thermalexpansion/contraction difference can be absorbed by deformation of theresilient member 508 or a relative shift between the frame 509 and theresilient member 508. Accordingly, separation of the frame 509 from theresilient member 508 (second electrode bar 504) can be prevented.

In the third embodiment, the concavities 509 a, 509 b are formed on theupper surface of the frame 509, and front end portions of the pressingscrews 510, 511 are fitted to the concavities 509 a, 509 b, whereby theframe 509 is fixed to the case 570, but the frame 509 may be fixed tothe case 570 without forming the concavities 509 a, 509 b on the uppersurface of the frame 509. For example, the front end portions of thepressing screws 510, 511 may be sharpened to make the front ends of thepressing screws 510, 511 cut into the upper surface of the frame 509.Alternatively, the front end portions of the pressing screws 510, 511may be fixed to the frame 509 by an adhesive. Further, enclosures (forexample, cylindrical projections) to enclose the surroundings of thefront end portions of the pressing screws 510, 511 may be formed on theupper surface of the frame 509.

Fourth Embodiment

FIG. 32A is a schematic plan view showing an internal structure of apower module according to a fourth embodiment of the present invention.FIG. 32B is a schematic side view of the internal structure of the powermodule shown in FIG. 32A.

The power module 521 shown in FIGS. 32A and 32B includes a heatradiating base 580 and a case 590. The case 590 is formed of aninsulating resin material.

Moreover, the power module 521 includes, for example, an IGBT chip 522which is a semiconductor chip with an IGBT. The IGBT chip 522 is formedin a rectangular shape in a plan view.

Moreover, the power module 521 includes a thin plate-like firstelectrode bar 523 and second electrode bar 524. The first electrode bar523 and the second electrode bar 524 are arranged on an insulating board581 provided on the heat radiating base 580. The first electrode bar 523and the second electrode bar 524 are provided side by side separatedfrom each other. These electrode bars 523, 524 are made of, for example,Cu (copper).

A surface at the collector side of the IGBT chip 522 is bonded to thefirst electrode bar 523 via a conductive adhesive 525 such as a solder.On a surface of the emitter side of the IGBT chip 522, an emitterelectrode 526 is formed.

On the emitter electrode 526, at a position one-sided to the secondelectrode bar 524 side, a resilient member 527 with conductivity isprovided. The resilient member 527 has the same configuration as that ofthe resilient member 507 shown in FIGS. 31A and 31B.

As shown in FIG. 32A, in the power module 521, two resilient members 527are provided, but the number of resilient members 527 are notparticularly limited, and it may be one, and may be three or more.

In addition, with the second electrode bar 524, a frame 528 isintegrally formed. The frame 528 extends from an end edge on the firstelectrode bar 523 side toward the above of the emitter electrode 526 ofthe IGBT chip 522. The frame 528 is bent at its halfway portion, and itsfront end portion is almost parallel to the emitter electrode 526, andis in pressure contact with the resilient members 527 on the emitterelectrode 526 from above. The emitter electrode 526 and the secondelectrode bar 524 are electrically connected via the resilient members527 and the frame 528.

A structure including the IGBT chip 522, the first electrode bar 523,the second electrode bar 524, the resilient member 527, and the frame528 is housed inside the case 590. In the case 590, a screw hole 591 isformed at a position facing the front end portion of the frame 528.Moreover, on an upper surface of the front end portion of the frame 528,a concavity 528 a is formed, in a plan view, at a position facing acenter portion of the screw hole 591. Into the screw hole 591 of thecase 590, a pressing screw 529 is fitted by screwing from above the case590. Then, a front end portion of the pressing screw 529 is fitted tothe concavity 528 a. A front end of the pressing screw 529 presses thefront end portion of the frame 528. Accordingly, the front end portionof the frame 528 presses the resilient member 527 by a pressing forcereceived from the pressing screw 529, and is reliably connected to theresilient member 527.

Also in the power module 521, the same advantageous effects as those inthe power module 501 shown in FIGS. 31A and 31B can be provided.

FIG. 33 is a schematic side view showing another configuration of aresilient member.

The resilient member 531 shown in FIG. 33 may be used in place of theresilient members 507, 508 shown in FIG. 31B and the resilient member527 shown in FIG. 32B. The resilient member 531 is formed by, forexample, bending into a V-shape a thin plate made of a metal such as Alor Au. When the resilient member 531 is used for the power module 501,521, one section of the resilient member 531 is joined to the emitterelectrode 506, 526, and the other section is pressed by the frame 509,528.

In the third embodiment or the fourth embodiment, the IGBT chip 502, 522having an IGBT has been mentioned as a semiconductor chip, but thesemiconductor chip may have an element such as a power MOSFET (MetalOxide Semiconductor Field Effect Transistor) or a diode.

Fifth Embodiment

FIG. 34 to FIG. 36B show a fifth embodiment of this invention. FIG. 34is an illustrative perspective view showing a configuration of a powermodule circuit housed inside a case. FIG. 35 is an illustrative planview showing first and second board assemblies. FIG. 36A is anillustrative sectional view of a first board assembly, and FIG. 36B isan illustrative sectional view of a second board assembly. In FIG. 34,the same parts as those in FIG. 2 are denoted by the same referencesigns as in FIG. 2. In FIG. 35, the same parts as those in FIG. 3 aredenoted by the same reference signs as in FIG. 3. In FIG. 36A or FIG.36B, the same parts as those in FIG. 5A or FIG. 5B are denoted by thesame reference signs as in FIG. 5A or FIG. 5B.

The power module according to the fifth embodiment has substantially thesame configuration as that of the power module according to the firstembodiment shown in FIG. 1 to FIG. 7B. In the power module according tothe fifth embodiment, an electrical connection structure between thefirst switching element Tr1 and the first diode Di1 and the first upperconductor layer 24 and an electrical connection structure between thesecond switching element Tr2 and the second diode Di2 and the secondupper conductor layer 44 are different from those of the firstembodiment.

In the fifth embodiment, a plate-shaped frame 210 is used in the firstboard assembly 20 in place of the wires 25, 26 used in the first boardassembly 20 of FIG. 2. The source of each first switching element Tr1and the anode of each first diode Di1 are, in the same manner as in thethird embodiment described by using FIG. 31A and FIG. 31B, via resilientmembers 221, 222 (refer to FIG. 36A) and the plate-shaped frame 210,connected to the first upper conductor layer 24 on the first upper board22.

As shown in FIG. 36A, on an upper surface (a +Z direction surface) ofeach first switching element Tr1 and an upper surface (a +Zdirection-side surface) of each first diode Di1, resilient members 221,222 with conductivity are provided, respectively. The resilient members221, 222 are the same as the resilient member 507 in the thirdembodiment described above. The resilient members 221, 222 are made of,for example, ribbon wires of Al (aluminum) or Au (gold).

The resilient member 221, as a result of being formed in a shape whoseboth ends are fixed to the upper surface of the first switching elementTr1 and whose central portion is floating up from the upper surface ofthe first switching element Tr1, is resiliently deformable at thecentral portion. Similarly, the resilient member 222, as a result ofbeing formed in a shape whose both ends are fixed to the upper surfaceof the first diode Di1 and whose central portion is floating up from theupper surface of the first diode Di1, is resiliently deformable at itscentral portion. Such resilient members 221, 222 may be providedindividually for each corresponding element, or two or more resilientmembers may be provided.

As shown in FIG. 34, FIG. 35, and FIG. 36A, the frame 210 is made of aconductive plate-like body (for example, Cu). The frame 210 has abonding portion 211 whose major portion is bonded to the first upperconductor layer 24, a pressure contact portion 213 that is in pressurecontact with the resilient members 221, 222 provided on the uppersurfaces of each first switching element Tr1 and each first diode Di1,and a joining portion 212 that joins the bonding portion 211 and thepressure contact portion 213.

The major portion of the bonding portion 211 is ultrasonic-bonded to aregion from the vicinity of a middle portion of the width in the Xdirection of the first upper conductor layer 24 to a +X direction-sideedge portion. The bonding portion 211 is formed in a rectangular shapeextending in the Y direction in a plan view. The bonding portion 211 ismade of a plate-like body parallel to the first upper conductor layer24, and its major part is bonded to the first upper conductor layer 24.The joining portion 212 extends in an intermediate direction between the+X direction and −Z direction from a +X direction-side edge portion ofthe bonding portion 211. The joining portion 212 is made of aband-shaped plate-like body.

The pressure contact portion 213 extends in the +X direction from a +Xdirection-side edge portion of the joining portion 212. The pressurecontact portion 213 is formed, in a plan view, in a U-shape having acut-away 214 opened toward the +X direction side. The pressure contactportion 213 has a base portion 213 a joined to the +X direction-sideedge portion of the joining portion 212 and a pair of arm portions 213b, 213 c extending in the +X direction from both end portions of thebase portion 213 a. The base portion 213 a is formed, in a plan view, ina rectangular shape extending in the Y direction. The base portion 213 afaces in the Z direction to a part of the upper surface of each of thetwo first diodes Di1 and a part of the upper surface of each of the twofirst switching elements Tr1 between those diodes Di1. The arm portions213 b, 213 c face in the Z direction to a part of the upper surface ofeach of the two first diodes Di1 and a part of the upper surface of eachof the two first switching elements Tr1 present on the +X direction sideof those diodes Di1.

The pressure contact portion 213 is in pressure contact from above withthe resilient members 221, 222 formed on the upper surface of each firstswitching element Tr1 and the upper surface of each first diode Di1.Specifically, with the resilient members 221 on the two first switchingelements Tr1 present on the +X direction side of the two first diodesDi1, the arm portions 213 b, 213 c of the pressure contact portion 213are in pressure contact. With the resilient members 221 on the two firstswitching elements Tr1 present between the two first diodes Di1, thebase portion 213 a of the pressure contact portion 213 is in pressurecontact. With the resilient members 222 on the two first diodes Di1, oneor both of the base portion 213 a of the pressure contact portion 213and the arm portions 213 b, 213 c is in pressure contact. Accordingly,the source of each first switching element Tr1 and the anode of eachfirst diode Di1 are electrically connected to the first upper conductorlayer 24 via the resilient members 221, 222 and the frame 210.

As shown in FIG. 36A, in the top plate 5 of the case 3, a plurality ofscrew holes 5 e are formed at positions facing the pressure contactportions 213 of the frame 210. It is preferable that a screw hole 5 e isformed, in a region of the top plate 5 facing the pressure contactportion 213, at each of the positions facing each first switchingelement Tr1 and each first diode Di1. Moreover, on an upper surface ofthe pressure contact portion 213, concavities 215 are formed, in a planview, at positions facing center portions of the screw holes 5 e. Intothe screw holes 5 e of the top plate 5, pressing screws 223 are fittedby screwing from above the top plate 5, respectively. Then, front endportions of the pressing screws 223 are fitted to the correspondingconcavities 215, respectively. A front end of each pressing screw 223presses the pressure contact portion 213 of the frame 210. Accordingly,the pressure contact portion 213 of the frame 210 presses the resilientmembers 221, 222 by pressing forces received from the pressing screws223, and are reliably connected to the resilient members 221, 222,respectively.

As shown in FIG. 34 and FIG. 35, a part of each first switching elementTr1 and a part of each first diode Di1 are exposed, in a plan view, fromthe cut-away 214 of the pressure contact portion 213. In the exposedpart of each first switching element Tr1, the source of each firstswitching element Tr1 is, via each wire 31, connected to the controllingconductor layer 27 for the source sense terminal SS1. Moreover, in theexposed part of each first switching element Tr1, the gate of each firstswitching element Tr1 is, via each wire 32, connected to the controllingconductor layer 28 for the gate terminal G1.

In the fifth embodiment, a plate-shaped frame 410 is used in the secondboard assembly 40 in place of the wires 45, 46 used in the second boardassembly 40 of FIG. 2. The source of each second switching element Tr2and the anode of each second diode Di2 are, via resilient members 421,422 (refer to FIG. 36B) and the plate-shaped frame 410, connected to thesecond upper conductor layer 44 on the second upper board 42.

As shown in FIG. 36B, on an upper surface (a +Z direction surface) ofeach second switching element Tr2 and an upper surface (a +Zdirection-side surface) of each second diode Di2, resilient members 421,422 with conductivity are provided, respectively. The configuration ofthe resilient members 421, 422 is the same as the configuration of theresilient members 221, 222 described above. Such resilient members 421,422 may be provided individually for each corresponding element, or twoor more resilient members may be provided.

As shown in FIG. 34, FIG. 35, and FIG. 36B, the frame 410 is made of aconductive plate-like body (for example, Cu). The frame 410 has abonding portion 411 whose major portion is bonded to the second upperconductor layer 44, a pressure contact portion 413 that is in pressurecontact with the resilient members 421, 422 provided on the uppersurfaces of each second switching element Tr2 and each second diode Di2,and a joining portion 412 that joins the bonding portion 411 and thepressure contact portion 413.

The major portion of the bonding portion 411 is ultrasonic-bonded to aregion from the vicinity of a middle portion of the width in the Xdirection of the second upper conductor layer 44 to a +X direction-sideedge portion. The bonding portion 411 is formed in a rectangular shapeextending in the Y direction in a plan view. The bonding portion 411 ismade of a plate-like body parallel to the second upper conductor layer44, and its major part is bonded to the second upper conductor layer 44.The joining portion 412 extends in an intermediate direction between the+X direction and −Z direction from a +X direction-side edge portion ofthe bonding portion 411. The joining portion 412 is made of aband-shaped plate-like body.

The pressure contact portion 413 extends in the +X direction from a +Xdirection-side edge portion of the joining portion 412. The pressurecontact portion 413 is formed, in a plan view, in a U-shape having acut-away 414 opened toward the +X direction side. The pressure contactportion 413 has a base portion 413 a joined to the +X direction-sideedge portion of the joining portion 412 and a pair of arm portions 413b, 413 c extending in the +X direction from both end portions of thebase portion 413 a. The base portion 413 a is formed, in a plan view, ina rectangular shape extending in the Y direction. The base portion 413 afaces in the Z direction to a part of the upper surface of each of thetwo second diodes Di2 and a part of the upper surface of each of the twosecond switching elements Tr2 between those diodes Di2. The arm portions413 b, 413 c face in the Z direction to a part of the upper surface ofeach of the two second diodes Di2 and a part of the upper surface ofeach of the two second switching elements Tr2 present on the +Xdirection side of those diodes Di2.

The pressure contact portion 413 is in pressure contact from above withthe resilient members 421, 422 formed on the upper surface of eachsecond switching element Tr2 and the upper surface of each second diodeDi2. Specifically, with the resilient members 421 on the two secondswitching elements Tr2 present on the +X direction side of the twosecond diodes Di2, the arm portions 413 b, 413 c of the pressure contactportion 413 are in pressure contact. With the resilient members 421 onthe two second switching elements Tr2 present between the two seconddiodes Di2, the base portion 413 a of the pressure contact portion 413is in pressure contact. With the resilient members 422 on the two seconddiodes Di2, one or both of the base portion 413 a of the pressurecontact portion 413 and the arm portions 413 b, 413 c is in pressurecontact. Accordingly, the source of each second switching element Tr2and the anode of each second diode Di2 are electrically connected to thesecond upper conductor layer 44 via the resilient members 421, 422 andthe frame 410.

As shown in FIG. 36B, in the top plate 5 of the case 3, a plurality ofscrew holes 5 f are formed at positions facing the pressure contactportion 413 of the frame 410. It is preferable that a screw hole 5 f isformed, in a region of the top plate 5 facing the pressure contactportion 413, at each of the positions facing each second switchingelement Tr2 and each second diode Di2. Moreover, on an upper surface ofthe pressure contact portion 413, concavities 415 are formed, in a planview, at positions facing center portions of the screw holes 5 f. Intothe screw holes 5 f of the top plate 5, pressing screws 423 are fittedby screwing from above the top plate 5, respectively. Then, front endportions of the pressing screws 423 are fitted to the correspondingconcavities 415, respectively. A front end of each pressing screw 423presses the pressure contact portion 413 of the frame 410. Accordingly,the pressure contact portion 413 of the frame 410 presses the resilientmembers 421, 422 by pressing forces received from the pressing screws423, and are reliably connected to the resilient members 421, 422,respectively.

As shown in FIG. 34 and FIG. 35, a part of each second switching elementTr2 and a part of each second diode Di2 are exposed, in a plan view,from the cut-away 414 of the pressure contact portion 413. In theexposed part of each second switching element Tr2, the source of eachsecond switching element Tr2 is, via each wire 51, connected to thecontrolling conductor layer 47 for the source sense terminal SS2.Moreover, in the exposed part of each second switching element Tr2, thegate of each second switching element Tr2 is, via each wire 52,connected to the controlling conductor layer 48 for the gate terminalG2.

Also in the fifth embodiment, the same effects as in the firstembodiment described above can be obtained. Further, in the fifthembodiment, the first switching element Tr1 and the first diode Di1 areelectrically connected to the first upper conductor layer 24 via theframe 210 for wiring in the first board assembly 20. The frame 210 has asectional area larger than that of bonding wires. For this reason, inthe fifth embodiment, the inductance can be reduced as compared withthat of a structure where the first switching element Tr1 and the firstdiode Di1 are electrically connected to the first upper conductor layer24 by wires. Accordingly, a surge voltage that occurs at the time ofturn-off of the switching element Tr1 can be reduced.

Between the first switching element Tr1 and the first diode Di1 and theframe 210, the resilient members 221, 222 are interposed. In addition, aconnection between the frame 210 and the elements Tr1, Di1 is achievednot by soldering but as a result of the resilient members 221, 222 beingpressed to the element Tr1, Di1 side by the frame 210.

Therefore, even if a thermal expansion/contraction difference occursbetween each element Tr1, Di1 and the frame 210, the thermalexpansion/contraction difference can be absorbed by deformation of theresilient member 221, 222 or a relative shift between the frame 210 andthe resilient member 221, 222. Thus, separation of the frame 210 fromthe resilient member 221, 222 (element Tr1, Di1) can be prevented.Moreover, propagation of a stress caused by a thermalexpansion/contraction difference between each element Tr1, Di1 and theframe 210 to each element Tr1, Di1 can be prevented. Accordingly, theoccurrence of cracks in each element Tr1, Di1 due to propagation of astress caused by a thermal expansion/contraction difference can beprevented.

Also with regard to the second board assembly 40, the same effects asthe effects of the first board assembly 20 as described above can beobtained.

In the fifth embodiment, the elements Tr1, Di1 on the first boardassembly 20 are connected to the first upper conductor layer 24 by thesingle frame 210, but the elements Tr1, Di1 on the first board assembly20 may be connected to the first upper conductor layer 24 by a pluralityof plate-shaped frames. For example, in place of the frame 210 describedabove, four frames in rectangular shapes whose widths in the Y directionare short in a plan view may be used. In this case, the four frames arearranged at intervals in the Y direction. One of the first diodes Di1present at the most −Y direction side and a first transistor Tr1 presenton its +X direction side are connected to the first upper conductorlayer 24 by a frame arranged at the most −Y direction side. The otherfirst diode Di1 present at the most +Y direction side and a firsttransistor Tr1 present on its +X direction side are connected to thefirst upper conductor layer 24 by a frame arranged at the most +Ydirection side. Two first transistors present between the two firstdiodes Di1 are connected to the first upper conductor layer 24 by thetwo remaining frames, respectively.

Similarly, the elements Tr2, Di2 on the second board assemblies 40 maybe connected to the second upper conductor layer 44 by a plurality ofplate-shaped frames.

Sixth Embodiment

FIG. 37 shows a sixth embodiment of this invention. FIG. 37 is anillustrative perspective view showing a configuration of a power modulecircuit housed inside a case. The power module according to the sixthembodiment has substantially the same configuration as that of the powermodule according to the fifth embodiment shown in FIG. 34. In FIG. 37,the same parts as those in FIG. 34 are denoted by the same referencesigns as in FIG. 34.

In the first board assembly 20, the source of each first switchingelement Tr1 and the anode of each first diode Di1 are, in the samemanner as in the fifth embodiment shown in FIG. 34, via the resilientmembers 221, 222 (not shown in FIG. 37) and the frame 210, electricallyconnected to the first upper conductor layer 24. The frame 210 is, asexplained in the fifth embodiment, made of a bonding portion 211, apressure contact portion 213, and a joining portion 212 that join those.Moreover, the frame 210 is formed integrally with a connecting member38. That is, a part closer to a −Y direction-side edge portion in a −Xdirection-side edge portion of the bonding portion 211 of the frame 210is joined to a +X direction-side edge portion of the bonding portion 58a of the connecting member 38.

In the second board assembly 40, the source of each second switchingelement Tr2 and the anode of each second diode Di2 are, in the samemanner as in the fifth embodiment shown in FIG. 34, via the resilientmembers 421, 422 (not shown in FIG. 37) and the frame 410, electricallyconnected to the second upper conductor layer 44. The frame 410 is, asexplained in the fifth embodiment, made of a bonding portion 411, apressure contact portion 413, and a joining portion 412 that join those.Moreover, the frame 410 is formed integrally with the second powersupply terminal N.

That is, a part closer to a +Y direction-side edge portion in a −Xdirection-side edge portion of the bonding portion 411 of the frame 410is connected to a −Z direction-side edge portion of the rising portion56 b of the second power supply terminal N. However, as compared withthe frame 410 of the fifth embodiment shown in FIG. 34, the frame 410 ofthis embodiment is extended in the +Y direction so that its +Ydirection-side edge portion is in alignment with a +Y direction-sideedge portion in the −Z direction-side edge portion of the rising portion56 b of the second power supply terminal N. Moreover, unlike the secondpower supply terminal N of the fifth embodiment, in the second powersupply terminal N of this embodiment, a bonding portion 56 a extendingin the −X direction from the −Z direction-side edge portion of therising portion 56 b does not exist.

In the sixth embodiment, the same effects as in the fifth embodiment canbe obtained. Further, in the sixth embodiment, the connecting member 38and the frame 210 are integrally formed, and the second power supplyterminal N and the frame 410 are integrally formed, so that the numberof components can be reduced, and manufacturing of a power module issimplified.

Seventh Embodiment

FIG. 38 shows a seventh embodiment of this invention. FIG. 38 is anillustrative perspective view showing a configuration of a power modulecircuit housed inside a case. In the power module according to theseventh embodiment, the shapes and arrangement of the terminals P, N,OUT are the same as the shapes and arrangement of the terminals P, N,OUT in the power module shown in FIG. 13. In FIG. 38, the same parts asthose in FIG. 13 are denoted by the same reference signs as in FIG. 13.

In the first board assembly 20, the source of each first switchingelement Tr1 and the anode of each first diode Di1 are, in the samemanner as in the fifth embodiment shown in FIG. 34, via the resilientmembers 221, 222 (not shown in FIG. 38) and the frame 210, electricallyconnected to the first upper conductor layer 24. The frame 210 is, asexplained in the fifth embodiment, made of a bonding portion 211, apressure contact portion 213, and a joining portion 212 that join those.Moreover, the frame 210 is formed integrally with the output terminalOUT. That is, a part closer to a −Y direction-side edge portion in a −Xdirection-side edge portion of the bonding portion 211 of the frame 210is joined to a +X direction-side edge portion of the bonding portion 151b of the output terminal OUT.

In the second board assembly 40, the source of each second switchingelement Tr2 and the anode of each second diode Di2 are, in the samemanner as in the fifth embodiment shown in FIG. 34, via the resilientmembers 421, 422 (not shown in FIG. 38) and the frame 410, electricallyconnected to the second upper conductor layer 44. The frame 410 is, asexplained in the fifth embodiment, made of a bonding portion 411, apressure contact portion 413, and a joining portion 412 that join those.Moreover, the frame 410 is formed integrally with the second powersupply terminal N. That is, a middle portion in the Y direction of a −Xdirection-side edge portion of the bonding portion 411 of the frame 410is joined to a +X direction-side edge portion of the bonding portion 160b of the second power supply terminal N.

In the seventh embodiment, the same effects as in the fifth embodimentcan be obtained. Further, in the seventh embodiment, the output terminalOUT and the frame 210 are integrally formed, and the second power supplyterminal N and the frame 410 are integrally formed, so that the numberof components can be reduced, and manufacturing of a power module issimplified.

Although the embodiments of the present invention have been described indetail, these are merely specific examples used to clarify the technicalcontents of the present invention, and the present invention should notbe interpreted as being limited to only these specific examples, and thescope of the present invention shall be limited only by the accompanyingclaims.

This application corresponds to Japanese Patent Application No.2009-230017 filed on Oct. 1, 2009 in the Japan Patent Office andJapanese Patent Application No. 2009-117271 filed on May 14, 2009 in theJapan Patent Office, and the entire disclosures of these applicationsare herein incorporated by reference.

REFERENCE SIGNS LIST

-   1 Power module-   2 Heat radiating base-   3 Case-   4 Frame portion-   5 Top plate-   6, 7 Side plate-   8, 9 End plate-   20 First board assembly-   Tr1 First switching element-   Di1 First diode element-   21 First lower board-   22 First upper board-   23 First lower conductor layer-   23 a Cut-away-   24 First upper conductor layer-   25, 26 Wire-   27, 28 Controlling conductor layer-   SS1 Source sense terminal-   G1 Gate terminal-   31, 32 Wire-   40 Second board assembly-   Tr2 Second switching element-   Di2 Second diode element-   41 Second lower board-   42 Second upper board-   43 Second lower conductor layer-   43 a Cut-away-   44 Second upper conductor layer-   45, 46 Wire-   47, 48 Controlling conductor layer-   SS2 Source sense terminal-   G2 Gate terminal-   51, 52 Wire-   P First power supply terminal-   N Second power supply terminal-   OUT Output terminal-   61 First terminal bonding area-   62 First element bonding area-   63 First board bonding area-   71 Second terminal bonding area-   72 Second element bonding area-   73 Second board bonding area-   81 Upper arm circuit-   82 Lower arm circuit-   110 Pedestal-   111 Lower surface of top plate-   113 Terminal retainer-   120 Power module-   123 Case-   124 Frame portion-   125 Top plate-   126, 127 Side plate-   128, 129 End plate-   135, 136 Bolt-   140, 141, 142 Slit-shaped insertion hole

The invention claimed is:
 1. A power module comprising: a first boardassembly; and a second board assembly, wherein the first board assemblyincludes: a first lower board having a first lower conductor layerformed on a surface thereof; a plurality of first semiconductor devicesbonded to the first lower conductor layer in a first element bondingarea; a first power supply terminal bonded to the first lower conductorlayer in a first terminal bonding area; and a first upper board stackedon the first lower board in a first board bonding area, and having afirst upper conductor layer on a surface thereof; the second boardassembly includes: a second lower board having a second lower conductorlayer formed on a surface thereof; a plurality of second semiconductordevices bonded to the second lower conductor layer in a second elementbonding area; an output terminal electrically connected to the firstupper conductor layer, and bonded to the second lower conductor layer ina second terminal bonding area; a second upper board stacked on thesecond lower board in a second board bonding area, and having a secondupper conductor layer on a surface thereof; and a second power supplyterminal bonded to the second upper conductor layer.
 2. The power moduleaccording to claim 1, wherein the first board assembly furthercomprising a first connecting member which connects the plurality offirst semiconductor devices with the first upper conductor layer; thesecond board assembly further comprising a second connecting memberwhich connects the plurality of second semiconductor devices with thesecond upper conductor layer.
 3. The power module according to claim 1,further comprising a case which surrounds the first board assembly andthe second board assembly, wherein a part of the output terminal is ledout of the case.
 4. The power module according to claim 3, wherein apart of the output terminal penetrates the side plate of the case and isled out of the case.
 5. The power module according to claim 4, wherein apart of the output terminal is elongated parallel to the second lowerboard and is led out of the case.
 6. The power module according to claim1, wherein the first power supply terminal and second power supplyterminal have plate-shaped parts facing each other with a predeterminedinterval kept therebetween.
 7. The power module according to claim 1,wherein the plurality of first semiconductor devices includes aplurality of first switching elements and a first diode element; theplurality of second semiconductor devices includes a plurality of secondswitching elements and a second diode element.
 8. The power moduleaccording to claim 7, wherein the first board assembly further comprisesa first switching element connecting member which connects the pluralityof first switching elements with the first upper conductor layer and iselongated parallel to a direction from the first element bonding area tothe first terminal bonding area; and a first diode element connectingmember which connects the first diode element with the first upperconductor layer, the second board assembly further comprises a secondswitching element connecting member which connects the plurality ofsecond switching elements with the second upper conductor layer and iselongated parallel to a direction from the second element bonding areato the second terminal bonding area; and a second diode elementconnecting member which connects the second diode element with thesecond upper conductor layer.
 9. The power module according to claim 7,wherein the plurality of first switching elements include a plurality offirst switching elements arranged spaced from the first diode element atalmost the same intervals around the first diode element and in adirection which is different from a direction opposed to one another;the plurality of second switching elements include a plurality of secondswitching elements arranged spaced from the second diode element atalmost the same intervals around the second diode element and in adirection which is different from a direction opposed to one another.10. The power module according to claim 9, wherein the first upperconductor layer is formed in a rectangular shape, the plurality of firstswitching elements are facing one side of the rectangular-shaped firstupper conductor layer, and the first switching elements include a pairof first switching elements facing both end portions of the one side ofthe first upper conductor layer; the second upper conductor layer isformed in a rectangular shape, the plurality of second switchingelements are facing one side of the rectangular-shaped second upperconductor layer, and the second switching elements include a pair ofsecond switching elements facing both end portions of the one side ofthe second upper conductor layer.
 11. The power module according toclaim 9, wherein the first diode elements includes a plurality of firstdiode elements; the first upper conductor layer is formed in arectangular shape, the plurality of first diode elements are facing oneside of the rectangular-shaped first upper conductor layer, and thefirst diode elements include a pair of first diode elements facing bothend portions of the one side of the first upper conductor layer; thesecond diode elements includes a plurality of second diode elements; thesecond upper conductor layer is formed in a rectangular shape, theplurality of second diode elements are facing one side of therectangular-shaped second upper conductor layer, and the second diodeelements include a pair of first diode elements facing both end portionsof the one side of the second upper conductor layer.
 12. The powermodule according to claim 7, wherein the first switching elements andsecond switching elements are elements using a SiC semiconductor.